International Conference on Integrated Waste Management and Green Energy Engineering (ICIWMGEE'2013) April 15-16, 2013 Johannesburg (South Africa)
Steady-state and dynamic load Performance of
Six -Phase Self-Excited Induction Generator
A. Senthil Kumar1, Josiah L Munda2, and G.K. Singh3
Using SPSEIG to divide the output power in two threephase groups allows for increased power in the drive system
and improves the reliability. The main advantage of this
configuration is that when failure happens in one of the threephase groups in the SPSEIG, the system can still operate at a
lower power rating. Another advantage is that the generator
supplies two separate three-phase loads, thereby improving
the real power output.
The first paper on the multi-phase induction generators
appeared in 2005 [7], followed by some more works on sixphase self-excited induction generator (SPSEIG) [8-11].
Authors in [9-11] have presented the modelling and analysis
of SPSEIG. In [9-11], performance evaluation of SPSEIG is
discussed showing its practical feasibility, whereas [12] deals
with the steady-state modelling and analysis of SPSEIG.
The paper is organized as follows; Section 2 presents an
explanation of the system under study; Section 3 is devoted to
the effect of Self-Excitation, voltage buildup and collapse
under no-load condition of SPSEIG; Section 4 deals with the
effect of speed variation; while Section 5 presents a summary
of the results.
Abstract— this paper presents steady-state and dynamic load
performance of a Six-Phase Self-Excited Induction Generator
(SPSEIG) with capacitor excitation used in stand-alone micro hydro
power generation. Detailed experimental investigations about the
voltage build-up, collapse of voltage, self-excitation of SPSEIG, and
operation with the capacitor connected in delta under no-load
condition and connection of purely resistive load are elaborated.
Keywords—self-excited induction generator,
excitation, renewable-energy generation, speed control.
capacitor
I. INTRODUCTION
E
NVIRONMENTAL concerns and international policies
are supporting new interest and development in smallscale power generation during the last few years [1]. Selfexcited induction generators have gained importance as they
are particularly suitable for wind and small hydro power
plants [2-3]. Interest in multi-phase drives has been steadily
increasing over the past 30 years, mainly due to the
advantages they possess over traditional three-phase drives.
These include improved reliability, reduced torque ripple,
increased torque density and reduction in inverter per-phase
rating [4].
When high-power levels are required, the use of six-phase
machines is one of the alternatives in industry. For variablespeed applications, power electronic converters are used to
drive the machine, and the power level of the converter has to
match the machine and the load. Limitations on the power
level of semiconductor devices present a barrier on the
increase in converter ratings [5]. In order to get rid of this
limitation, multilevel converters have been developed where
switches of reduced rating are used to construct high-power
level converters. Instead of multilevel converters, multi-phase
machines can be used. By dividing the handled power
between multiple phases, generally more than three, highpower levels can be achieved even by using limited rated
power electronic converters. Multi-phase systems expand the
universe for drive and control purposes [6].
II. SYSTEM UNDER STUDY
A simplified schematic diagram of the experimental setup
is shown in Fig.1. SPSEIG is connected across a delta
connected capacitor bank, single three-phase winding set abc
and both winding sets abc and xyz through miniature circuit
breaker(mcb) and subjected to separate three- phase star
connected variable resistances through a contactor connected
for both sets. The series capacitor as shown in Fig 1 is needed
in order to improve the voltage regulation in SPSEIG.
In the Fig.1 provision is made for alternative exploitation
(in this experimental setup) of the machine as six phase output
or three phase output. SPSEIG allows for the operation at
adjustable speeds, which is sensed and display by a micron
[mode: 2176] speed transducer and digital encoder range [609999] rpm unit. Fluke 43b is used to measure voltage, current,
power and transient waveform.
The induction machine used in this study is 50 Hz, 6 poles,
960 rpm, 1.1 kW, 2.9 A, 415 V, 36 slot squirrel case. All the
72
armature
coil
terminals
were
taken
out
A.Senthil Kumar1, Department of Electrical Engineering, Tshwane
University of Technology, Pretoria-0001, South Africa. (corresponding author
to provide phone: +27743559011; e-mail: vastham@gmail.com,
Senthilkumara@tut.ac.za ).
Josiah L Munda2, Department of Electrical Engineering, Tshwane
University of Technology, Pretoria-0001, South Africa..
G.K. Singh3, Department of Electrical Engineering, Indian Institute of
Technology, Roorkee-247 667, India.
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International Conference on Integrated Waste Management and Green Energy Engineering (ICIWMGEE'2013) April 15-16, 2013 Johannesburg (South Africa)
Cseries a
MCB
b
Six phase
SEIG V
b
Contactor
Va Vc
x
30°
1:1:1 T/F
a
Excitation capacitor
Cshunt
z
b
IL
L
O
A
D
c
x
c
y
Vy
y
Vx
Vz
Contactor
MCB
Cseries
Prime Mover
z
Fig. 1 Schematic diagram of the induction generator system employing a six-phase self-excited induction generator
on a connection table mounted on the top of the machine body
to give way for different winding schemes for the different
number of poles and phases. The layout of the stator winding
of the SPSEIG can be made as split phase winding
configuration. In this configuration six phase stator winding
can be made by two equal parts of star connected three phases
winding sets (namely xyz and abc respectively) with spatial
phase separation of 30 electrical degrees. In this configuration
of stator winding design, there is a strong magnetic coupling
between the stator phases. Here, neutral points of two threephase sets of stator windings have been isolated, in an attempt
to prevent physical fault propagation from one three phase set
to the other one, and to avoid the flow of triplen harmonics.
The test machine was coupled to a semi closed-loop small
hydro power (SHP) plant. The SHP test rig [8,9], consists of
two identical service pumps, each having 150 litres per
second discharge capacity at the head of 10 meters, connected
to a 5kW cross-flow turbine of efficiency 56% through
pipeline networks. The measured parameters of the test
machine in p.u. are: R s1 =R s2 = 0.1198, R rr =0.2576,
X s1 =X s2 = 0.1987,X r = 0.3985 From the magnetization curve
as described in [8], the following approximation by the
polynomial of degree 3 can be made: E g /F =- K 1 X m 3 +
K2Xm2 – K3Xm + K4
Where, K 1 = 0.0002, K 2 = 0.0657, K 3 = 8.0427, K 4 = 550
TABLE I.
INDUCTION MACHINE DATA FROM THE TESTS
Six-phase induction machine data
Resistances
inductance at 50 Hz
R s =4.095Ω
Stator leakage inductance L ls= 25mH
R r =7.79 Ω
Rotor leakage inductance L lr =25mH
6 pole
Mutual inductance L m =241 mH
Frequency=50 Hz
Rated power=1.1kW
Further synchronous speed test has been carried out by
means of a dc drive coupled to the induction machine. This
test adds to the accuracy as it ensures zero slip.
III. SELF-EXCITATION, VOLTAGE BUILDUP AND COLLAPSE
UNDER NO-LOAD CONDITION OF SPSEIG
A. Effect of voltage buildup and voltage collapse of
SPSEIG at no load
Table II and Table III show the analytical results for
voltage build up and collapse for three values of excitation
capacitance, when the capacitor bank is connected to one of
its three-phase winding sets, and when the capacitor bank is
connected to both winding sets.
TABLE II
VOLTAGE BUILD-UP AND COLLAPSE WHEN DELTA C-BANK IS CONNECTED
ACROSS WINDING SET ABC AT NO LOAD.
One of its three phase winding set is connected
Excitation
across C-bank
C-bank
Experimental results
Analytical results
Voltage
Voltage
Voltage
Voltage
buildup
collapse
buildup
collapse
50µF
780 rpm
650 rpm
750 rpm
650 rpm
41µF
850 rpm
750 rpm
830 rpm
750 rpm
32µF
925 rpm
800 rpm
900 rpm
800 rpm
A. Parameter Determination Test
A no-load circuit test and blocked rotor tests are performed.
The parameters of the induction generator are computed from
the test data, and the results are listed in Table I.
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International Conference on Integrated Waste Management and Green Energy Engineering (ICIWMGEE'2013) April 15-16, 2013 Johannesburg (South Africa)
TABLE III
VOLTAGE BUILD-UP AND COLLAPSE WHEN DELTA C-BANK CONNECTED
ACROSS BOTH WINDING SET ABC AND XYZ AT NO LOAD
Excitation Cbank
30µF
25µF
20µF
Both winding set is connected across C-Bank
Experimental results
Analytical results
Voltage
Voltage
Voltage
Voltage
buildup
collapse
buildup
collapse
650 rpm
475 rpm
650 rpm
600 rpm
700 rpm
550 rpm
730 rpm
650 rpm
800 rpm
650 rpm
800 rpm
700 rpm
B. Establishment of self- excitation
Fig.2 illustrates the voltage and current transients across the
three-phase winding set abc with the other three phase
winding set xyz kept open. The SPSEIG is operating at 1000
rpm with the delta connected capacitor bank switched on
across the winding set abc. SPSEIG was found to be selfexcited smoothly even with the excitation at the one three
phase winding set. This is of course a consequence of the
strong magnetic coupling between the two three phase
windings.
b.
Fig.3.Self-excitation transients ;(a) voltage and current build-up
across winding set abc of SPSEIG after switching on the delta
connected bank of C sh = 25 µF at both winding sets abc and xyz, (b)
voltage and current build-up across winding set xyz of SPSEIG after
switching on the delta connected bank of C sh = 25 µF at both
winding sets abc and xyz.
Here, both winding sets abc and xyz have the delta
connected capacitor bank switched on at the same time at an
operating speed of 1000 rpm. Voltage and current build up
are illustrated in Fig.3a and Fig.3b. Simultaneously, excitation
at both winding sets pushes the operating point at the
magnetization curve into deeper saturation.
IV. EFFECT OF SPEED VARIATION
For this work, the six-phase to the three-phase transformer
shown in Fig.1, was not utilized and each three-phase
winding set (abc and xyz) was independently loaded with a
specific resistive load. Contactors were provided to enable
switching of the delta connected three-phase shunt capacitor
to either only one of the three-phase winding sets or to both
winding sets. The series capacitors, C se shown in Fig.1, were
also removed during experimentation as a simple shunt.
Experimental investigations are carried out for a simple shunt
connected across winding set abc for different modes of
operation, and when it is connected to both winding sets abc
and xyz. The speed of the prime mover can be varied with
specific resistive loads as elaborated in the next section.
a.
A. Variation of speed, while the one three- phase winding
set abc connected across shunt capacitance (C sh =41 µF) with
a resistive load and the other winding set xyz is kept open
The SPSEIG can be loaded with a resistive load by closing
the switch across abc winding at a given capacitance value,
and the speed of the prime mover varied. Fig.1 allows for the
collection of information about the relationship between load
at winding set abc, the exciting capacitor at winding set abc
and the speed. It shows the allowable speed range, and the
generated voltages are improved by increasing the load
resistance. If the load increases (resistance decreases) the
voltage drops and may go to zero if the speed is not
readjusted. For each curve, a careful evaluation of X m equal to
the slope of the air-gap line will give an appreciation of the
lower limit of the speed range beyond which the machine
becomes unstable and losses its voltage, the higher limit being
determined by the ratings of the machine.
Fig.4a shows the values of voltage build up against speed
for specific load resistance. It is seen that for each load
resistance there exist a minimum and maximum speed beyond
which voltage buildup with that specific terminal resistance is
b.
Fig.2 Self-excitation transients; (a) voltage and current build-up
across winding sets abc of SPSEIG after switching on the delta
connected bank of C sh =41µF at set abc only, (b) voltage and current
build-up across winding set xyz of SPSEIG after switching on the
delta connected bank of C sh =41µF at set abc only.
a.
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International Conference on Integrated Waste Management and Green Energy Engineering (ICIWMGEE'2013) April 15-16, 2013 Johannesburg (South Africa)
Load voltage for different value
of R
impossible. Fig.4b shows the rotor speed versus frequency
with specific load resistance.
Fig.5a illustrates the terminal voltage and current transients
at winding set abc that follows the speed changes from 1000
to 900 rpm, whose load is R L =440 ohm. Fig.5b. illustrates the
terminal voltage and current transients at winding set abc
that follows speed changes from 900 to 1000 rpm, whose load
is R L =440 ohm.
The variation in voltage and current with the change in
speed for different loading conditions is depicted in table IV
for steady-state reference. The same percentage change
(reduction and increase respectively) in voltage and current
was recorded for both conditions, i.e, when speed changes
from 1000 to 900 rpm and also when speed changes from 900
to 1000 rpm.
b.
Fig.5 voltage and current transients at winding set abc with R L =440
ohm. (a) when speed changes from 1000 rpm to 900rpm, (b) when
speed changes from 900 rpm to 1000 rpm.
TABLE IV
VARIATION IN VOLTAGE AND CURRENT WHEN SPEED CHANGES FROM 1000 TO
900 RPM AT DIFFERENT RESISTIVE LOADING:
Speed
Voltage
Current
R load
reduction % reduction %
reduction %
880 ohm
10
17
15
440 ohm
10
19
13
220 ohm
10
25
10
230
200
1-RL=880 ohm
2-RL=440 ohm
3-RL=220 ohm
3
2
170
140
1
110
B. Variation of speed, both winding sets abc and xyz
connected with shunt capacitance (C sh1 = C sh2 = 25µF) and
subjected to separate resistive loading
Fig. 6a shows the variation of load voltage as a function of
rotor speed when both the three-phase winding sets abc and
xyz are excited. Characteristic curves are given for three
different values of load resistances, R L = 154ohm, 281ohm
and 563ohm. It is observed that load voltage decreases with
the decrease in speed. Fig 6b. shows the variation of
frequency as a function of rotor speed when both the threephase winding sets abc and xyz are excited for three different
values of load resistances, R L = 154ohm, 281ohm and
563ohm. It is noticed that the frequency decreases with
decrease in rotor speed.
Fig.7 illustrates the voltage and current transients for both
winding sets, when speed changes from 1000 rpm to 900 rpm.
In Table V, the variation of speed from 1000 to 900 rpm is
elaborated at three different values of resistance. It is clear
from the table that with the speed reduction from 1000 to 900
rpm for the three values of load resistance, voltage regulation
is improved as the load resistance increases.
80
50
750
800
850
900
950
1000
rotor speed(rpm)
frequency for different value of R
a.
50
3
2
40
1
30
20
750
1-RL=880 ohm
2-RL=440 ohm
3-RL=220 ohm
800
850
900
950
1000
rotor speed(rpm)
load voltage for different value of R
(V)
b.
Fig.4. Variation of load voltage (a), and frequency (b), as the
function of rotor speed for different values of load resistance when
winding set abc excited by shunt capacitance Csh=41µF is subjected
to specific resistive load with winding set xyz kept open.
230
200
170
1-RL=563 ohm
2-RL=281 ohm
3-RL=154 ohm
3
2
140
1
110
80
50
800
850
900
rotor speed(rpm)
6 a.
a.
295
950
1000
frequency for differenct value of
R (Hz)
International Conference on Integrated Waste Management and Green Energy Engineering (ICIWMGEE'2013) April 15-16, 2013 Johannesburg (South Africa)
of the proposed method. The specific conclusions of this
paper are summarized as follows.
1. The proposed methods provide the ability to analyze
the unregulated behaviour of the SPSEIG with any
prime mover by considering the effects of
unregulated prime mover on the system performance.
2. For a loaded SPSEIG, there are also limiting values,
which determine the range of C, u, and the load
impedance over which self-excitation can be
maintained. These extreme values can be computed
by following the proposed method of analysis.
60
3
50
1
2
40
30
20
1-RL=563 ohm
2-RL=281 ohm
10
3-RL=154 ohm
0
800
850
900
950
1000
rotor speed (rpm)
6 b.
Fig.6. Variation of load voltage (a) and frequency (b) of SPSEIG
against rotor speed when the capacitor banks are connected to
winding sets abc and xyz.
REFERENCES
[1]
B. Palle, M. G. Simoes and F. A. Farret,”Dynamic simulation and
analysis of Parallel self-excited induction generator for islanded wind
frame systems,” IEEE Tans. Ind. Applicat., vol. 41, no. 4, pp. 1099–
1106, July/Aug. 2005.
[2] F. A. Farret, B. Palle and M. G. Simoes,” Full expandable model of
parallel self-Excited induction generators,” IEE Proc.-Electr. Power
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[3] Singh, G. K., “Self-excited induction generator research – a survey,”
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[4] Singh, G. K., “Multi-phase induction machine drive research – a
survey,” Electric Power Systems Research, Vol. 61, pp. 139-147, 2002
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torque control of six-phase induction machine with special phase current
waveform,” in Conf. Rec. IEEE IAS Annu. Meeting, Tampa, FL,
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[6] Jones, M., and Levi, E., “A literature survey of state-of-the-art in multiphase ac drives,” Proc. 36th Univ. Power Eng. Conf. UPEC 2002,
Stafford, U.K., pp. 505-510.
[7] Singh, G. K., Yadav, K. B., and Saini, R. P., “Modeling and analysis of
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Conf. The Eighth International Conference on Electrical Machines and
Systems, ICEMS’05, Vol. 3, pp.1922-27, September 27-29, 2005.
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Journal of Emerging Electric Power Systems, Vol. 7, pp.1-23, 2006.
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a.
b.
Fig.7. voltage and current transients at both windings sets excited
with R L =563ohm and (a) when speed changes from 1000 rpm to 900
rpm (b) when speed changes from 900 rpm to 1000 rpm
TABLE V.
VARIATION IN VOLTAGE AND CURRENT WHEN SPEED CHANGES FROM 1000 TO
900 RPM AT DIFFERENT RESISTIVE LOADING
R Load
Speed
Voltage
Current
reduction %
reduction %
reduction %
560 ohm
10%
20%
19%
280 ohm
10%
25%
15%
153 ohm
10%
27%
13%
288-297.
V. CONCLUSION
This paper has discussed steady-state and dynamic load
performance of Six-Phase Self-Excited Induction Generator
(SPSEIG) with capacitor excitation used in stand-alone micro
hydro power generation. Effects of self-excitation, shunt
capacitance, load impedance and speed have been studied.
This paper has also presented both experimental and
simulated results of the studied SPSEIG to validate the results
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