ieee_pecon_1569336945_4_

8/8/2019 IEEE_pecon_1569336945_4_

http://slidepdf.com/reader/full/ieeepecon15693369454 1/6

Steady State Investigation of Self Excited 3

Phase Induction Generator with Novel

Leading VAR Controller and Mitigation of

Harmonics Using Active Power Filter Vargil Kumar E

Department of EEE, Gudlavalleru

Engineering College, Gudlavalleru,

A.P. 521 356, INDIA

[email protected]

Narasimham PVRLDepartment of EEE, Gudlavalleru

Engineering College, Gudlavalleru,

A.P. 521 356, INDIA

[email protected]

Sarma AVRSDepartment of Electrical Engg.,

Osmania University, Hyderabad,

A.P. 520 001, INDIA

[email protected]

Abstract – Self Excited Induction Generator (SEIG) is

identified as isolated power source, whose terminal voltage

and frequency are controlled by varying speed, excitation

capacitance or load impedance. Since load changes from

time to time, the output parameters mostly are controlledby either speed or by varying excitation capacitance. To

reduce the complexity in analysis, the speed of a prime-

mover driving the induction generator is kept constant. For

proper voltage built-up suitable value of excitation

capacitance is necessary.

This paper presents a method for calculating the

minimum excitation capacitance using the equivalent

circuit approach for analyzing the steady state operation of

SEIG. Change in load impedance forces alteration in the

value of excitation capacitance which is difficult to be

implemented. A novel leading VAR controller (LVARC)

consisting of uncontrolled converter, inverter and a series

LCR resonance circuit, is introduced in between the load

and source to take care of reactive power disparity thereby

feeding the reactive power to the inductive loads andabsorbing reactive power for capacitive loads.

A closed loop operation of SEIG was developed using

Shunt Active Power Filter (SAF) is used for harmonic

elimination.

MATLAB based simulation and experimental results

are presented and compared for VAR controller operated

with linear loads. Simulation study is made for Non-Linear

loads with respect to SAF’s. The simulation results show

the effectiveness of Voltage built-up and harmonic

reduction in Wind based Power Generation.

Key words: SEIG, Leading VAR Controller, Shunt Active Power

Filter (SAF), Harmonics.

I I NTRODUCTION

The depleting Energy resources had made the present

society to rethink about the Power generation procedures

and paved a path for utilizing Non-renewable energy

resources [1]. One such resource is Wind Energy, where

the generated output power varies as the cube of wind

speed shown in Fig.1.

3

2

1ν ρ A pC P = (1)

Where ρ is the air density, ‘C p’ is the power coefficient

and ‘A’ is the rotor swept area and ‘v’ is the wind speed

Basically the wind generation schemes involve

induction generators, not only of its usage in large

numbers but also due to varied modes of operation both

under steady and dynamic states. Increased use of Power

Electronic controllers with such machines makesappropriate modeling and parameter identification

crucial, for both working control strategies and

performance predictions.

Induction Generator (IG) is not able to start on its

own and sustain electrical oscillations. To sustain the

electrical oscillations, reactive magnetization current

should be completely compensated by appropriate

reactive current [2, 3]. It is well known that a suitable

capacitor is compulsory to be connected at the output

terminals of induction machine while working as

generator, which raises a problem in designing the value

of capacitor. This paper confers a simple nevertheless

open methodical procedure to perceive the steady statecondition using the operational equivalent circuit of the

machine [5, 6].

SEIG has to supply both the linear and non-linear

loads. As a result, the reactive power oscillation has to

take place between the source and the load, which

enforces the VAR control, envisaging the usage of

power electronic switching devices and passive energy-

storage-circuit elements inductors or capacitors. These

elements can be used for controlling current harmonics

at the low or medium-voltage distribution levels or for

controlling reactive power, and voltage [7-10].

Fig1. Speed and Power Output Characteristic

2010 IEEE International Conference on Power and Energy (PECon2010)., Nov 29 - Dec 1, 2010, Kuala Lumpur, Malaysia

978-1-4244-8945-9/10/$26.00 ©2010 IEEE 495

8/8/2019 IEEE_pecon_1569336945_4_


In a capacitance excited SEIG, the terminal voltage

and its frequency are dependent on exciting capacitance,

speed and load impedance. The required exciting

capacitance calculation for a load impedance is

estimated through a MATLAB program, by keeping the

prime mover speed as constant.

II THEORY OF PROPOSED VAR CONTROLLER

With the designed capacitance, and constant prime-

mover speed the terminal voltage of IG reaches torequired voltage.

The controller consists of three parts – the front

end uncontrolled rectifier, the SPWM inverter and the

LCR series circuit shown in Fig. 2. The VAR controller

circuit is used in conjunction with the fixed minimum

capacitance, which is permanently connected to the

machine terminals. With increase in load the capacitance

required to sustain the terminal voltage increases, this

increase in the reactive power requirement.

Change in the load current will insist to change

AC/DC/AC resonance circuit current in opposite

direction. The total generator current should be

maintained at the rated current. At any instant of time

AC/DC/AC converter is operated to balance the load

current to maintain the generator current constant. The

variable frequency operation of series resonance LCR

circuit effectively takes care of VAR variation in load,

which is supplied by the VAR controller by operating

the inverter either below or above the resonant

frequency.

Because of proposed VAR controller, the power

factor variation of SEIG is minimized. The mathematical

approach in relation to above discussion is given in the

commencing section.

III MODELING OF PROPOSED VAR CONTROLLER

The advantage in this scheme is that only, fixed

minimum capacitance is needed to be connected to the

SEIG, and also this scheme provides smooth terminal

voltage regulation. The per phase equivalent circuit

given in Fig.3, is taken to derive the expression for

terminal capacitance.

Here core losses are being ignored. For the

minimum capacitance requirement, the machine must

operate at the threshold of saturation. All the parameters

except ‘Xm’ magnetizing reactance are assumed

constant.

The voltage in the loop PQRS can be written as

0=eqloop Z . I (2)

The loop equivalent impedance “Zeq” of SEIG with

proposed controller is given by reducing the circuit

around the loop PQRS

⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢

⎣

⎡

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎥⎦

⎤⎢⎣

⎡+⎟⎟

⎠

⎞⎜⎜⎝

⎛

−

+

⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ ⎥⎦

⎤⎢⎣

⎡+⎟⎟

⎠

⎞⎜⎜⎝

⎛

+

⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎟⎟ ⎠

⎞

⎜⎜⎝

⎛ −

⎥⎦

⎤

⎢⎣

⎡−+

⎟⎟ ⎠

⎞

⎜⎜⎝

⎛

⎥⎦

⎤

⎢⎣

⎡+

=

mr r

s s

ct csh

lsh

sh

ll

l

jX jX f

R jX

f

R

f

jX

f

jX

jX f

R

jX f

R

eq Z

ν

22

(3) On solving and combining similar terms in eq.3 a

complex equation in terms of terminal capacitive

reactance ‘X ct ’ frequency ‘f’ is achieved.

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

−+

+−

+

+

−−++++−

−++−

=

4v)E j(f 3 E

2 jE 1v)E (f

f

2 jfB1 B

+

ct X 11 fA )10 Act X 9(A2

jf )8 Act X 7 (A3

f 6 A4

jf 5 A5

f

)4 A3 jfA2 A2

f 1 A3

jf ( ct X

eq Z

(4)

Under steady state self excitation the loop current is not

zero,( 0≠loop I ), so equivalent impedance is assumed

to be zero [6]. The real and imaginary parts of ‘Z eq’ are

zeros. From eq. 4 separating the real and imaginary parts

of the terminal capacitance ‘ X ct ’ are obtained as

11102

93

84

75

62

53

44

35

26

17

fM M f M f M f M f

M f M f M f M f M f M f

real ct X

++++

+++++

= (5)

982

73

64

52

43

34

25

16

fI I f I f I f

I f I f I f I f I f

imag ct X +++

++++

=

(6)

The terminal capacitance is to be calculated it should

simultaneously satisfy both eq.5 and eq.6. is obtained by

equating both of them, resulting in a 11 th order equation

in ‘ f ’.

93

84

75

66

57

48

39

210

111

J f J f J f J f J f J f J f J f J f ctl X ++++++++=

(7)

Fi .2 Pro osed VAR controller with SEIG

Fig. 3 Equivalent circuit of SEIG with proposed controller.

496

8/8/2019 IEEE_pecon_1569336945_4_


The solution of the eq.7 is tedious and lengthy a

MATLAB m-file program was written and solved. By

conducting suitable tests, and using the basic equations

of induction machine the proposed VAR controller is

designed, and open loop operation is being assessed for

linear loads and nonlinear loads, by verifying the

theoretical and experimental results and are presented in

section VIII.

Operation of LVARC happened to an open loopsystem is effective with respect to linear, but coming to

nonlinear loads the harmonic current are not properly

taken care because of presence of fast acting nonlinear

switching devices (as shown in Fig.13, Fig. 18 can be

compared). So a closed loop system based on shunt

active power filter is designed, the discussion follows.

IV CLOSED LOOP SAF DESIGN FOR SEIG

When SEIG supplies a non-linear load, the load

draws a fundamental component of current and harmonic

current from the generation systems, which are to be

properly controlled. The shunt APF can compensate the

harmonic current by continuously tracking the changesin harmonic content. APF’s consists of a voltage fed

converter with a PWM current controller and an active

filter controller that realizes an almost instantaneous

control algorithm shown in Fig.4.

The SAF works in a closed loop manner,

continuously sensing the load current and calculating the

instantaneous values of the compensating current

reference I c* for the PWM converter. In an ideal case,

the PWM converter may be considered as a linear power amplifier, where the compensating current I c tracks

correctly its reference I c*.

V MATHEMATICAL MODELING OF SAF-SEIG

The source voltages in all the three phases are

combined with currents, are converted to Vα ,Vβ , and Iα

,Iβ by using Clarke Transformation. These space vectors

are easily transformed into a three coordinates as follows

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡ −

=

⎥⎥⎦

⎤

⎢⎢⎣

⎡

cvb

v

av

23

1/2

23

1/2

0

1

3

2

β v

αv

(9)

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡ −

=

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

cibi

ai

23

1/2

23

1/2

0

1

3

2

β i

αi

The conventional instantaneous power on the three phase

circuit can be defined by using ‘p-q’ theory as

β β α α .iv.iv += p (10)

Instantaneous reactive power is defined by

αββα .iv.ivq += (11)

The conventional instantaneous power, ‘p’ and the

Instantaneous imaginary power ‘q’, are expressed by

⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

−=⎥

⎦

⎤⎢⎣

⎡

β

α

α β

β α

i

i

vv

vv

q

p

(12)After determining the active and reactive power signals,

they are smoothened by passing through a low pass

filter. Later they are converted back to three phase

reference currents and made available for comparison

with actual currents. Both are fed to Hysteresis Current

Controller (HCC) where the firing angle corresponding

to the difference of the two signals is generated and fed

to Inverter shown in Fig. 5.

The inverter is enabled to act as a filter and the use of

inductive and capacitive elements can be vanished out,thereby reducing the cost involved on them (as in case of

LVARC). And this filter design promises the closed loop

control and provides better efficient harmonic

elimination, which is validated by simulation results.

VI SIMULATION METHODOLOGY

The required capacitance value (C = 105.2 µFd) of

SEIG has been calculated from the steady state

Fig. 4 Block Diagram of APF

Fig. 5 A Three phase, Three-wire, Current Compensation SAF

497

8/8/2019 IEEE_pecon_1569336945_4_


equivalent circuit, using MATLAB m-file program by

solving a 11th order equation in ‘X ct ’ , and simulation of

SEIG with proposed VAR controller and the closed loop

operation with SAF is being done using simpower

systems block-set of MATLAB/Simulink. The Simulink

models of SEIG with LVARC and SAF is shown in

Fig.6, Fig.7 and results of LVARC are presented in Fig.8

to Fig.10 for linear loads and Fig. 11 to Fig. 12 for

Nonlinear loads. The results of SAF with Non-linear loads are presented in Fig. 16 for Voltage built-up;

variation of voltage, current in Fig. 17; and Pulse

Generation using current controller in Fig. 18.

VII R ESULTS

A 3-φ, 3 KVA, 415V, 7A alternator is connected

across R-L load, and a drop of about 45V is calculated to

be controlled. For convenience the voltage waveform in

the graphs from 8 to 11 are scaled by 5, in order to get a

better view of voltages and currents.

0.56 0.57 0.58 0.59 0.6 0.61 0.62

-10

0

10

S o u r c e

O u t p u t

0.56 0.57 0.58 0.59 0.6 0.61 0.62

-10

0

10

C o n t r o l l e r

O u t p u t

0.56 0.57 0.58 0.59 0.6 0.61 0.62

-10

0

10

Time in Seconds

L o a d

O u t p u t

0.56 0.57 0.58 0.59 0.6 0.61

-5

0

5

S o u r c e

O u t p u t

0.57 0.58 0.59 0.6 0.61 0.62

-10

0

10

C o n t r o l l e r

O u t p u t

0.56 0.57 0.58 0.59 0.6 0.61 0.62-10

-5

05

Time in Seconds

L o a d

O u t p u t

0.56 0.57 0.58 0.59 0.6 0.61

-5

0

5

S o u r c e

O u t p u t

0.57 0.58 0.59 0.6 0.61 0.62

-5

0

5

C o n t r o l l e r

O u t p u t

0.56 0.57 0.58 0.59 0.6 0.61 0.62-10

-5

0

5

Time in Seconds

L o a d

O u t p u t

0.6 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.7

-5

0

5

S o u r c e O u t p u t

0.6 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.7

-5

0

5

C o n t r o

l l e r O u t p u t

0.6 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.7

-5

0

5

Time in Seconds

L o a d O u t p u t

Fig. 10 Leading VAR Control of proposed Controller

Fig. 8 Lagging VAR Control of proposed Controller

Fi . 9 In- haseVAR Control of ro osed Controller simulation

Fig. 7 Simulation of SEIG with Active Power Filter and HysteresisCurrent Controller with non-linear Load

Fig. 11 Leading VAR Control of proposed Controller with

Nonlinear Loads

Fig. 6 Simulation of SEIG with proposed VAR controller

498

8/8/2019 IEEE_pecon_1569336945_4_


0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74

-5

0

5

V o l t a g e o f P h a s e ' a '

o f L V A R C

0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74

-5

0

5

Time in Seconds

C u r r e n t i n p h a

s e ' a '

o f L V A R C

VIII POWER QUALITY A NALYZER R ESULT The observed phasors are obtained using the

FLUKE power quality analyzer and are given in Fig.13

to Fig.15. The variable impedance effect of the LCR

series circuit with the change in inverter output

frequency was observed. 0.6 0.62 0.64 0.66 0.68 0.7

-4

-2

0

2

4

V o l t a g e

i n

p h a s e

' a ' o f S A F

0.6 0.62 0.64 0.66 0.68 0.7

-4

-2

0

2

4

Time in Seconds

C

u r r e n t i n

p h a s e

' a ' o f S A F

0.6 0.62 0.64 0.66 0.68 0.7

-2

0

2

C

u r r e n t i n

' A ' p h a s e

0.6 0.62 0.64 0.66 0.68 0.7

-4-202

D i s t o t e d

C u r r e n t

0.6 0.62 0.64 0.66 0.68 0.7

-202

E r r o r

C u r r e n t

0.6 0.62 0.64 0.66 0.68 0.7

0

0.5

1

Time in Seconds

H y s t e r e s i s

P u l e s e s

IX CONCLUSION

It can be accomplished that the minimum

excitation capacitance calculated from the design

equations was found to be 105.2µF, which aided proper

Fig. 14 Lagging effect at frequencies greater than

resonant fre uenc

Fig. 18 Waveforms of Reference currents, Controller Current, Error

current and H steresis ulse Generation

Fig. 16 Voltage built-up in all the three phases of SEIG-SAF

Fig. 17 Stator Voltages and currents in phase ‘A’ of SAFwith non linear loads.

Fig. 15 Leading effect at frequencies greater than

resonant frequency

Fig. 12 Stator Voltages currents in phase ‘A’ of

LVARC with non linear loads

Fig. 13 UPF effect at frequencies equal to resonant

499

8/8/2019 IEEE_pecon_1569336945_4_


voltage built-up in an SEIG. The novel LVARC

introduced between SEIG and load has taken care of the

reactive power disparity by providing a reactive power

ranging from 10% to 40% of the rated capacity on an

average, feeding linear and non-linear loads. An

improvement in the voltage magnitude and power factor

is possible by changing the operating frequency of the

inverter in multiples of 50Hz, and the by varying LCR

component ratings above and below 35mH and 291 µF.The shunt active power filter with the aid of

hysteresis current controller had taken care of the uneven

distortion in current thereby smooth voltage

characteristic at the output is achieved in comparison

with LVARC technique. The Shunt active power filter

eliminated the harmonics by enabling the inverter to act

as a filter, fading away the usage of inductors and

capacitors, reducing the cost involved on them.

The simulation and experimental results proves

the effectiveness of VAR controller, and Shunt Active

Power Filter in Wind based Power System.

APPENDIX

By performing various tests on a 3φ squirrel cage

induction machine possessing a rating of 3.7KW, 415V,

50Hz the stator resistance and inductances were found

to be 0.057, and 0.001 p.u., and Rotor 0.04 and 0.001

p.u., and magnetizing reactance of 1.93 p.u. is preferred.

Expansion of various terms used in the equation are

given below

lshl ll sh

lshll

cshl

lshll lshl

ll shlshl

lshll

X R X R A

X X A X R A

X X R R A

X R X R A

X X A

+=

=

=

+=

+=

+=

6

5

4

3

2

1

csh

shl

cshl

lshll

cshll shl

X A

R R A

X R A

X X A

X X R R A

=

+=

=

+=

+=

11

10

9

8

7

)(

)(*

14366

135

3512344

33113

322

311

vQQM

QM QQvQM

QQM

vQM

QM

+−=

=

−+=

+=

−=

=

)(

)(*

170511

5516045410

0353159

02528

517

QQM

QQQvQM

QQQM

vQQM

QM

+−=

−−−=

++=

+=

=

255

2442414

40233

2239382

37211

)(*

)(*

Q I

QQvQ I

QQ I

QQvQ I

QQ I

=

−+=

−=

−+−=

−=

)(*

)(*

29099

28088

59582707517

5626066

QQv I

QQ I

QQQQvQ I

QQQ I

−=

−=

+++−=

++=

J1=(M1I6-M7I1)

J2=M1I7+M2I6-(M8I1+M7I2)

J3=M1I8+M2I7+M3I6-(M9I1+M8I2-M7I3)

J4=M1I9+M2I8+M3I7+M4I6-(M8I3+M9I2+M10I1+M7I4)

J5=M2I9+M3I8+M4I7+M5I6-

(M8I4+M9I3+M10I2+M11I1+M7I5)

J6=M3I9++M4I8+M5I7+M6I6-(M8I5+M9I4+M10I3+M11I2)

J7=M4I9+M5I8+M6I7-(M9I5+M10I4+M11I3)

J8=M5I9+M6I8-(M10I5+M11I4)

J9=M6I9-M11I5

R EFERENCES

1. Iulian Munteanu • Antoneta Iuliana Bratcu, Nicolaos-Antonio

Cutululis • Emil Ceang “Optimal control of Wind EnergySystems” , Springer Edn., 2007.

2. P.Vas, Electrical Machines and Drives – A Space Vector Approach, Oxford: Clarendon Press, 1992..

3. R.Rabinovici, “Autonomous excitation of induction generators”,

IEEE transactions on Mag., v.34, pp. 664-670, May 1998.

4. G.R.Slemon, Electric Machines and Drives, Reading, MA:

Addison-Wesley Publishing Company, Inc., 1992.5. Kh. Al Jabari and Alolah “ Limits on the performance of the Three

Phase Self-excited Induction Generators”, IEEE Transaction on

energy Conversion, vol.,5, No.2, Page 350-356,June 1990.

6. Kh. Al Jabari and Alolah, “Capacitance requirement for Self-excited Induction Generator”, IEE Proceeding, Vol.137, pt. C,

No.3, Page 154-159,May 1990. 7. S. Singaravelu, S. Velusami, “Capacitive VAR requirements for

wind driven self-excited induction generators”, Energy

Conversionand Management 48 (2007) 1367–1382.

8. Hirofumi Akagi, Yoshihira Kanazawa, and Akira Nabae.:

‘Instantaneous Reactive Power Compensators Comprising Switching Devices without Energy Storage Components’ , IEEE

Transactions on Industry Applications, Vol. IA-20, No. 3,

June1984.9. Jayant K. Chatterjee, B.Venkatsa Perumal, and Naveen Reddy

Gopu “Analysis of Operation of a Self Excited InductionGenerator with Generalized Impedance Controller”, IEEETrans. Power App. Sys., vol.22 No.2, pp. 307-315, 2006.

10. Bhim Singh, S.S. Murthy, and Sushma Gupta, “Analysis and Design of Electronic Load Controller for Self-Excited InductionGenerators”, IEEE Trans. On Energy Conversioon, Vol.21,

No.1, Page 285-294, March 2006.

500

ieee_pecon_1569336945_4_

Documents