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Power System Stability Improvement byEnergy Storage Type STATCOM

Kazuhiro Kobayashi, Masuo Goto, Fellow IEEE, Kai Wu, Member IEEE,

Yasunobu Yokomizu, Member IEEE and Toshiro Matsumura, Member IEEE

Abstract — This paper describes an approach to design a damping con-

troller of an energy storage type STATCOM. The energy storage type

STATCOM (ESTATCOM) is an advanced flexible ac transmission sys-

tem (FACTS) device, which controls both reactive and active power in-

jection/absorption to the power system. It also provides a better power

swing damping. Using a linearized block diagram proposed by the authors,

the present study examines the design of the ESTATCOM damping con-

troller. Several case studies have been performed to evaluate the power

swing damping effect of the ESTATCOM on one-machine infinite bus sys-

tem. The results of the study show that an ESTATCOM, which controls

both reactive and active power injection/absorption to power system, has a

more significant effect on power swing damping than that controlling the

reactive power alone.

Keywords— Power system stability, Flexible ac transmission system

(FACTS), Static synchronous compensator (STATCOM), Energy storage,

Linearized model

I. INTRODUCTION

IN recent years, the electric power system has grown in size

and complexity with a huge number of interconnections to

meet the increase in the electric power demand. Moreover, the

role of long distance and large power transmission lines become

more important. However, the constructions of new transmis-

sion lines are becoming difficult due to economical, social and

environmental problems.On the basis of the above background, many flexible ac trans-

mission system (FACTS) technologies have been developed.

Furthermore, as a typical FACTS device, static synchronous

compensators (STATCOMs) have been developed and put into

operation to maintain voltage and to improve the power swing

damping by reactive power control [1]-[2]. In other words, a

STATCOM can be used to enhance the power quality provided

to consumers by decreasing voltage flicker and correcting small

voltage sags. Also, it has been shown that a STATCOM with

a new controller can be used to handle unbalanced voltages in

distribution power systems [4]. As an example of insertion of

STATCOM into a power system, a STATCOM is currently in-stalled at Inuyama Switching Substation in Japan and the Sul-

livan Substation of the Tennessee Valley Authority (TVA) for

transmission line compensation [3][5].

The active power injection/absorption control function has bet-

ter performance for the power swing damping and can improve

the transient stability. But STATCOM itself cannot control the

Kazuhiro Kobayashi, Yasunobu Yokomizu are with the Department of Elec-trical Engineering, Nagoya University, Nagoya, Japan. Furo-cho, Chikusa-ku,Nagoya, Japan. 464-8603, Tel : (+81) 52-789-3637, Fax : (+81) 52-789-3134,E-mail : [email protected].

Masuo Goto and Kai Wu are with Center for Integrated Research in Scienceand Engineering, Nagoya University, Nagoya, Furo-cho, Chikusa-ku, Nagoya,Japan. TEL : (+81) 052-789-2098, FAX : (+81) 052-789-5374, E-mail :

[email protected].

active power injection/absorption to power system. A STAT-

COM with energy storage system can control both the reactive

and the active power injection/absorption, thus providing more

flexible power system operation [6]. Recently, the development

of high output energy storage devices have made it possible to

generate or absorb the active power. As an illustration, it has

been shown that a STATCOM with SMES as energy storage

source can be very effective in damping power system oscil-

lations [7]. As energy storage devices, the authors have consid-

ered advanced batteries and an ECS (energy capacitor system;advanced electric double layer). In this paper, the authors call

the STATCOM with energy storage function an ESTATCOM.

This paper presents a newly developed linearized block dia-

gram of a power system with an ESTATCOM which represents

the dynamics of power system. A design method for the damp-

ing controller of the ESTATCOM using the linearized block di-

agram was described. Several simulations have been done to

show the effect of the designed ESTATCOM damping controller

on the power system oscillation stability. The active and reactive

power responses of the compensator to oscillations were also es-

timated.

II. POWER S YSTEM M ODEL

A. Model of ESTATCOM

As can be seen in Fig. 1, the ESTATCOM is represented by

a current source for both active and reactive compensator. The

damping controllers of the active and the reactive current con-

trol the output of each current source separately. Each damping

controller consists of a detector of input signal, a filter, a phase

compensator, a gain and a limiter.

Fig. 1. Block diagram of ESTATCOM.

0-7803-7967-5/03/$17.00 ©2003 IEEE

Paper accepted for presentation at 2003 IEEE Bologna Power Tech Conference, June 23th-26th, Bologna, Italy

8/10/2019 ACE93D87d01


Fig. 2. Confi gurationof input and output of ESTATCOM.

As illustrated in Fig. 2, the voltage deviation signal ∆E mat the bus where ESTATCOM is connected and the active power

flow deviation signal ∆P L on the transmission line were consid-

ered as input signals.

B. Model of Power system

Figure 3 shows the power system used in this study. In this

model, the infinite bus is represented by a constant source volt-

age having a constant frequency. An ESTATCOM is connected

to the bus N2 between the generator terminals and the infinite

bus. In this figure, the reactance of the line from the generatorterminals to the bus N2 is xe1 and the reactance of the line from

the bus N2 to the infinite bus is xe2. The resistance of the line is

neglected. The terminal voltage and the phase voltage are illus-

trated in the figure.

The exciter system of the generator is shown in Fig. 4. It is a

typical thyristor exciter system. The control constants are given

in TABLE V. The power system stabilizer is not applied.

Fig. 3. Power system model with an ESTATCOM.

Fig. 4. Block diagram of exciter system (Ge(s)).

III. LINEARIZED BLOCK DIAGRAM OF POWER SYSTEM

WITH ESTATCOM

A linearized block diagram, which represents the dynamic be-

haviors of the power system with an ESTATCOM, has been de-

veloped to design the damping controller of the ESTATCOM

and to analyze the dynamics of the system. The newly devel-

oped linearized block diagram is obtained by extending Heffron

and Phillips model [8][9] which represents the dynamics of a

synchronous machine, including the dynamics of the ESTAT-

COM [10]-[12]. The outline about Heffron and Phillips model

is given in Appendix B. To develop a linearized block diagram,

the following assumptions were made.

(1) Initial value of each current from the ESTATCOM is zero.

(2) Phase and magnitude of the voltage behind xd is assumed

to remain constant just after disturbance.

According to Heffron and Phillips model, the deviation of the

bus voltage ∆E m at N2 may be expressed as

∆E m = K 7∆δ + K 8∆ψfd (1)

where ∆δ is deviation of rotor angle, ∆ψfd is deviation of field

flux linkages. From Eq. (1), K 7 and K 8 are the sensitivity con-

stants, the so called K constants, and are given by the following

equations,

K 7 = emd0

E m0

·

(xq + xe1)

xq + xe1 + xe2

E s cos δ 0

−

emq0

E m0

·

(xd + xe1)

xd + xe1 + xe2

E s sin δ 0 (2)

and

K 8 = emq0

E m0

·xe2

xd + xe1 + xe2

(3)

where each symbol is defined in Appendix A.

As can be seen in Fig. 1, both active and reactive compensators

of the ESTATCOM are represented by a current source. So, the

system with an ESTATCOM is expressed by an equivalent cir-

cuit as shown in Fig. 5.

The relationship between the voltage deviations ∆E m, ∆E Tand the injected reactive current ∆I Q from ESTATCOM are ex-

pressed as follows.

∆E m = K Q1∆I Q (4)

∆E T = K Q2∆I Q (5)

Since E is constant just after disturbance, using Eq. (4), the

deviation active power output ∆P e from generator is,

∆P e = xe2

xd + xe1 + xe2

E sin(δ − δ m0)∆I Q = K Q3∆I Q (6)

The constants K Q1, K Q2, K Q3 shown above are given as fol-

lows,

K Q1 = (xd + xe1)xe2

xd + xe1 + xe2

(7)

K Q2 =

xdxe2

xd + xe1 + xe2 (8)

K Q3 = xe2

xd + xe1 + xe2

E sin(δ − δ m0) (9)

Fig. 5. Equivalent circuit of power system model with an ESTATCOM.

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Injecting only a small active current ∆I P from an ESTATCOM,

the voltage deviations ∆E T, ∆E m and the deviation of active

power output ∆P L from the generator are given,

∆E m = K P1∆I P (10)

∆E T = K P2∆I P (11)

∆P e = K P3∆I P (12)

where K P1, K P2, K P3 are given by the following expressions,

K P1 = E m0

E

x

d+xe1

cos(δ − δ m0) + E s

xe2cos δ m0

(13)

K P2 = E m0x

d

E cos(δ − δ m0) + x

d+xe1

xe2E s cos δ m0

(14)

K P3 = E m0E

cos(δ − δ m)

E cos(δ − δ m0) + x

d+xe1

xe2E s cos δ m0

(15)

Combining the above equations, a linearized block diagram is

obtained which expresses the dynamic behaviors of the powersystem with an ESTATCOM, as seen in Fig. 6. Figure 6 shows

an example of the developed model where the voltage deviation

signal ∆E m of N2 and the active power flow deviation ∆P L of

the transmission line are used as the input signal for the ESTAT-

COM damping controllers.

Fig. 6. Block diagram of one-machine infi nitebus system with an ESTATCOM.

IV. DESIGN OF DAMPING CONTROL SYSTEM FOR

ESTATCOM

A. Sensitivity constants of a model power system

TABLE I summarizes the value of the sensitivity constants

expressed by Eqs. (2), (3), (7)-(9), (13)-(15) and (A1)-(A6).

These values are calculated under the system condition shown in

Fig. 9 described in the next section. The dynamic characteristics

of the system are expressed by the block diagram shown in Fig. 6

with the sensitivity constants.

TABLE I

SE N S I T I V I T Y C O N S T A N TS O F M O D E L P O W E R S Y S T E M.

K 1 = 1.11 K 2 = 1.07 K 3 = 0.380

K 4 = 1.44 K 5 = –0.0682 K 6 = 0.459

K 7 = –0.0991 K 8 = 0.286 K Q1 = 0.181

K Q2 = 0.127 K Q3 = 0.137 K P1 = 0.184

K P2 = 0.129 K P3 = 0.476

Fig. 7. Vector diagram of torques.

B. Out line of design method

In this paper, the feedback control theory is applied to de-

sign the damping control system for the ESTATCOM shown in

Fig. 1. The outline is described as follows.

The change in electrical torque of a synchronous machine ∆T e

can be resolved into two components:

∆T e = T S∆δ + T D∆ω (16)

where T S∆δ is the component of the torque change in phase

with the rotor angle perturbation ∆δ and is referred as the syn-

chronizing torque component and T D∆ω is the component of

the torque change in phase with the speed deviation ∆ω and is

referred as the damping torque component .

As illustrated in Fig. 7, a positive damping torque component

represents the decay of oscillation. The larger is its magnitude,

the faster is the decay. On the other hand, a negative damping

torque component represents instability.

To provide damping, the ESTATCOM must produce a com-ponent of electrical torque from ESTATCOM ∆T EST in phase

with the rotor speed deviation ∆ω. However, as shown in Fig. 6,

the torque ∆T Ex is influenced due to the current from the ES-

TATCOM by the coefficient K P2 and K Q2. The compensa-

tion for the phase of the ESTATCOM’s damping controller also

changes the torque component of ∆T Ex.

The damping controller of the ESTATCOM should have an

optimal phase compensation for both torque ∆T Ex and torque

∆T EST to generate a good damping torque component.

C. Design of ESTATCOM damping controller

TABLE II shows the control schemes for the ESTATCOM.

As described in the previous section, the time constants of the

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TABLE II

CONTROL SCHEM ES.

Case Input signal Output

Case 0 - -

Case 1 ∆E m Q

Case 2 ∆P L Q

Case 3

∆E m

∆P L

Q

P

TABLE III

DE S I G N E D C O N T R O L C O N S TA N T S O F ESTATCOM .

Case 1

T Q1 = 0.02 sec T Q2 = 0.106 sec T Q3 = 0.02 sec

T Q4 = 0.02 sec K Q = 7.15 ULQ = 0.1 pu

LLQ = –0.1 pu

Case 2


T Q4 = 0.154 sec K Q = 150 ULQ = 0.1 pu

LLQ = –0.1 pu Case 3


T Q4 = 0.02 sec K Q = 7.15 ULQ = 0.1 pu

LLQ = –0.1 pu T I = 7.0 sec T P1 = 1.0 sec

T P2 = 0.02 sec T P3 = 0.071 sec T P4 = 0.065 sec

T P5 = 0.02 sec K P = 300 ULP = 0.1 pu

LLP = –0.1 pu

phase compensator in the damping controller of ESTATCOM

were determined. In addition, concerning the capacity of the

ESTATCOM output, the limiter values and the gain of the damp-ing controllers were determined. The parameters of the damping

controller for the ESTATCOM are shown in TABLE III.

Figure 8 illustrates the comparison of change in electrical

torque ∆T e of a synchronous machine in case of applying each

control scheme at 1 Hz region of power swing. The case where

the ESTATCOM is not introduced into the power system is de-

noted as Case 0. In this case, the damping torque is negative, so

the amplitude of the power swing may increase.

As shown in Fig. 8, controlling the ESTATCOM can add a

Fig. 8. Comparison of change in the electrical torque∆T e of generator for each

case at 1 Hz region of power swing.

positive damping torque component. Case 1 and Case 2 repre-

sent a situation where the ESTATCOM only controls the reac-

tive power injection/absorption. In Case 1, the voltage devia-

tion ∆E m at N2 is used as the input signal for the ESTATCOM

damping controller. This case results in a slight increase in the

damping torque. In Case 2, the active power flow deviation ∆P Lof the line is used as the input signal for the ESTATCOM. In

this case, the damping torque is improved compared with Case1. However, the effect of damping may be insufficient.

In Case 3, the ESTATCOM controls both active and reactive

power injection/absorption to the bus where an ESTATCOM

is installed. In this case, the active power injection/absorption

is controlled by ∆P L signal and the reactive power injec-

tion/absorption is controlled by ∆E m signal. As shown in

Fig. 8, in Case 3, the damping component of the torque ∆T eis significantly increased compared with Case 1 and Case 2.

Hence, installing an ESTATCOM in a power system is expected

to provide a large damping effect.

V. CONFIRMATION OF POWER SWING DAMPING

IMPROVEMENT BY DIGITAL SIMULATION

A. Power system model and constants

Simulation studies for the evaluation of damping effects by

the ESTATCOM have been performed on a one-machine infinite

bus system shown in Fig. 9. The values of the circuit parameters

used in this study are given in this figure. The specifications

of the synchronous generator are summarized in TABLE IV.

Fig. 9. Initial power flow of assumed power system.

TABLE IV

SPECIFICATIONS OF SYNCHRONOUS GENERATOR.

Generator type Thermal

Rated capacity 1100 MVA

Rated active power output 1000 MW

Rated voltage 100 kV

d-axis synchronous reactance xd 1.70 puq-axis synchronous reactance xq 1.70 pu

d-axis transient reactance xd 0.35 pu

q-axis transient reactance xq 0.35 pu

d-axis subtransient reactance xd 0.25 pu

q-axis subtransient reactance xq 0.25 pu

d-axis transient time constant T d 1.00 sec

q-axis transient time constant T q 0.206 sec

d-axis subtransient time constant T d 0.03 sec

q-axis subtransient time constant T q 0.03 sec

Armature reactance xl 0.225 pu

Armature time constant T a 0.40 sec

Per unit inertia constant H 3.5 MW·sec/MVA

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TABLE V

CO N T R OL C O N S TA N T S O F AVR.

T A1 = 0.10 sec T A2 = 0.05 sec T A3 = 0.2 sec

K A = 150 ULA1 = 100 pu LLA1 = –100 pu

ULA2 = 5.0 pu LLA2 = –5.0 pu

Fig. 10. Operating condition of ESTATCOM.

The control constants of the exciter shown in Fig. 4 are given in

TABLE V.A three-phase-to-ground fault is assumed to occur at bus N2 in

Fig. 9 at a time of 1.0 sec and to be cleared 70 msec after fault

occurrence.

B. Operating condition of ESTATCOM during disturbance

In this simulation, the ESTATCOM is considered to stop its

operation when the voltage of the bus E m where the ESTAT-

COM is connected becomes lower than a preset threshold value.

On the other hand, the ESTATCOM is to restart after 30 msec

when the bus voltage recovers the preset threshold value. This

operating condition is shown in Fig. 10. In this figure, the preset

threshold value is set at 0.5 pu of the voltage E m.

C. Results of simulation

Digital simulation studies were performed to evaluate the ef-

fect of the ESTATCOM control schemes from the viewpoint of

improvement of power swing damping. A comparison among

four control schemes was given in TABLE II.

Figure 11 indicates the swing curves of the generator rotor

angle in the presence and in the absence of the ESTATCOM.

Moreover, in the presence of the ESTATCOM, three different

cases (Case 1, 2 and 3) were considered and compared with that

in the absence of the ESTATCOM. As can be seen in Fig. 11(a),

the oscillation damping slightly decreases by controlling the re-active power injection/absorption of a conventional STATCOM

where the deviation of voltage ∆E m at bus N2 is used as input

signal.

Figure 11(b) presents the swing curves of the generator rotor

angle in the case where the ESTATCOM only controls the reac-

tive power and the deviation of active power flow ∆P L of the

line is used as the input signal. In this case, for a same ES-

TATCOM, we can see that the damping effect is improved in

comparison with the case where the deviation of voltage ∆E mwas used as the input signal.

The swing curves of the generator rotor angle for an ESTAT-

COM controlling both active and reactive power are illustrated

in Fig. 11(c). From this figure, it can be seen that the ES-

Fig. 11. Swingcurve of generator rotor angle in the presenceof an ESTATCOM.

TATCOM which controls both active and reactive power injec-

tion/absorption decreases the oscillation faster than that control-

ling only the reactive power injection/absorption.

The results of this simulation show that applying an ES-

TATCOM which controls both active and reactive power injec-

tion/absorption provides a stronger damping of oscillation than

applying a conventional STATCOM which controls only the re-

active power injection/absorption.

TABLE VI shows the damping of the main oscillation modecalculated for each case indicated in TABLE II from the wave-

forms given in Fig. 11.

TABLE VI

CO N T R OL S C H E M E S A N D D A M P I N G O F M A I N O S C I L LAT I O N M O D E.

Case Input signal Output damping (1/sec)

Case 0 - - –0.348×10−3

Case 1 ∆E m Q 0.283

Case 2 ∆P L Q 0.608

Case 3 ∆E m

∆P L

Q

P 1.219

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Fig. 12. Active and reactive power injection/absorption from ESTATCOM.

The active and reactive power responses of the compen-

sator to oscillations for an ESTATCOM controlling both active

and reactive power injection/absorption (Case 3) are given in

Fig. 12(a) and (b), respectively. From the waveforms exhibited

in Fig. 12(a), the capacity of injected electrical energy from the

ESTATCOM to stabilize the power system was found to be 50

MW·sec. This result shows that 50 MW·sec energy storage sys-

tem can improve the damping of 1000 MVA generator signifi-

cantly. For a same enhancement in oscillation damping, it seems

that the size of a 50 MW·sec-energy storage system which is to

be connected to the STATCOM is not so large compared to the

size of an energy storage system alone. In other words, as far as

the results of the present study are concerned, considering the

significant improvement of stability that the STATCOM-energy

storage combination can bring to a 1000 MVA-generator, the 50

MW·sec energy storage system may be cost-effective.

V I. CONCLUSIONS

This paper proposes a linearized block diagram of a power

system with an energy storage type STATCOM (ESTATCOM)

and the control schemes for the ESTATCOM. The ESTAT-

COM, which controls both reactive and active power injec-

tion/absorption, has a more significant effect on the oscillation

damping compared to that controlling only the reactive power

injection/absorption. From the active and reactive power re-

sponses of the compensator to oscillations for an ESTATCOM, it

was found that the necessary energy storage capacity to improve

the power swing damping is not so large, thus the additional cost

for the energy storage system is expected to be small.

VII. APPENDIX

A. Nomenclature

I P : Active current from ESTATCOM, in per unit

I Q : Leading reactive current from ESTATCOM, in pu

E d : Voltage of behind xd, in pu

E T : Terminal voltage of generator, in pu

E m : Voltage of bus N2, in puE s : Voltage of infinite bus, in pu

E fd : Field voltage, in pu

ed , eq : d-axis and q-axis component of E T, in pu

emd , emq : d-axis and q-axis component of E m, in pu

δ : Generator rotor angle (radian)

δ : Phase angle of E (radian)

δ T : Phase angle of E T (radian)

δ m : Phase angle of E m (radian)

ω0 : Rated rotor speed, in radian/sec. 60π in west Japan

ω : Rotor speed deviation based on ω0, in pu

ψfd : Field flux linkages, in pu

T m : Mechanical torque, in puT Ex : Torque from exciter, in pu

T EST : Torque from ESTATCOM, in pu

T e : Electrical torque of the generator (T EX + T EST), in pu

B. Heffron and Phillips model

Figure 13 shows the block diagram of representation of dy-

namic characteristics of the system called Heffron and Phillips

model [8][9]. K 1 - K 6 are K constants indicated by Eq. (A1) -

(A6) using the initial steady-state values of system variables.

Fig. 13. Heffron and Phillips model.

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K 1 = E q0E s

xq + xe

cos δ 0 + xq − xd

xq

·

edoE s

xd + xe

sin δ 0 (A1)

K 2 = E s

xd

+ xe

sinδ 0 (A2)

K 3 = xd + xe

xd + xe

(A3)

K 4 = xd − xdx

d + xe

E s sin δ 0 (A4)

K 5 = ed0E s

E T0

·

xq

xq + xe

cos δ 0

−

eq0E s

E T0

·

xdx

d + xe

sin δ 0 (A5)

K 6 = eq0

E T0

·

xe

xd

+ xe

(A6)

REFERENCES

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[2] S. Mori, K. Matsuno, T. Hasegawa, S. Ohnishi, M. Takeda, M. Seto, S.Murakami, F. Ishiguro : “Development of a Large Static VAR GeneratorUsing Self-Commutated Inverter for Improving Power System Stability,”IEEE Trans. Power Systems, Vol. 8, No. 1, pp. 371-377, Feb 1993.

[3] T. Sato, Y. Mori, Y. Matsushita, S. Ogusa, N. Morishima, N. Toki, I. Iy-oda : “Study on the System Analysis Method of STATCOM based on Ten-Years’ Field Experience,” IEEE/PES Transmission and Distribution Con-ference and Exhibition 2002: Asia Pacifi cConference Proceedings Vol. 1,pp. 336-341, 2002.

[4] C. Hochgraf and R. H. Lasseter : “Statcom Controls for Operation withUnbalanced Voltages,” IEEE Trans. on Power Delivery, Vol. 13, No. 2, pp.538-544, April 1988.

[5] N. G. Hingorani and L. Gyugyi, “Understanding Concepts and Technologyof Flexible AC Transmission Systems,” 1999, IEEE Press, pp. 394-407.

[6] C. Qian, M. L. Crow : “A Cascaded Converter-Based StatCom with EnergyStorage,” 2002 IEEE Power Engineering Society Winter Meeting, No.03-3488-0054, 2002.

[7] A. B. Arsoy, Y. Liu, P. F. Ribeiro, F. Wang : “Static-Synchronous Compen-sators and Superconducting Magnetic Energy Storage Systems in Control-ling Power System Dynamics,” IEEE Industry Applications magazine, Vol.

9, No. 2, pp. 21-28, March/April 2003.

[8] W. G. Heffron and R. A. Phillips : “Effect of Modern Amplidyne VoltageRegulator in Underexcited Operation of Large Turbine Generators,” AIEETrans, Vol.PAS-71, pp. 692-697, August 1952.

[9] C. Concordia : “Steady-State Stability of Synchronous Machines as Af-fected by Voltage Regulator Characteristics,” Electrical Engineering AIEETrans, Vol. 63, pp. 215-220, May 1944.

[10] P. Kundur : “Power System Stability and Control,” 1993, McGraw-Hill,Inc., pp. 737-748.

[11] H. F. Wang : “Applications of damping torque analysis to STATCOM con-trol,” International Journal of Electrical Power and Energy Systems 22, pp.197-204, 2000.

[12] H. F. Wang, F. J. Swift : “A Unifi ed Model for the Analysis of FACTSDevices in Damping Power Oscillations Part I: Single-machine Infi nite-busPower Systems,” IEEE Trans. Power Delivery, Vol. 12, No. 2, pp. 941-946,

April 1997.

Kazuhiro Kobayashi was born in Kosyoku, Japan, on June 12, 1978. He re-

ceived a bachelor’s degree in Electrical Engineering from Nagoya University

in March 2002, Japan. He is currently a graduate student in Electrical Engi-

neering at Nagoya University, Japan. His research concerns the technology for

stabilizing control of power system by exciter system of generator and by power

electronics device. He is a member of the Institute of Electrical Engineers of

Japan.

Masuo Goto received the B.S and the Ph.D. degrees from University of Osaka

prefecture, Japan in 1965 and 1979, respectively. He received Professional En-

gineer degree from the Institution Professional Engineers, Japan in 2001. He

joined Hitachi Research Laboratory of Hitachi, Ltd. in 1965. From 1965 to

2000 he was engaged in research and development in the fi eldof power system

analysis, control and protection. In 2001, he moved to Nagoya University. He

is currently a Guest Professor of Nagoya University. He received the Advanced

Technology Award of IEE of Japan for the development of an advanced power

system simulator in 1991. He is an IEEE fellow and a member of the Institute

of Electrical Engineers of Japan.

KaiWu received M.S. andPh.D degrees from Xi’an Jiaotong University in 1992

and 1998, respectively. From 1995 to 1997, he studied as an exchange student at

Electrical Departmentin Nagoya University, Japan. He worked as a postdoctoral

research fellow at Nagoya University from 1998 to 2000, and is now a research

associate of Nagoya University at Center for Integrated Research in Science and

Engineering. He is a member of IEEE and a member of the Institute of Electri-

cal Engineers of Japan.

Yasunobu Yokomizu received the Ph.D. degree in Electrical Engineering from

Nagoya University, Japan in 1991. He was an Assistant Professor at Nagoya

University in the Department of Electrical Engineering from 1990 to January

2000. Since February 2000, he has been an Associate Professor at Nagoya Uni-

versity in the same department. He is presently involved in the study of various

phenomena and technologies related to the electric power system. He is a mem-ber of IEEE and a member of the Institute of Electrical Engineers of Japan.

Toshiro Matsumura received the Ph.D. degree in Electrical Engineering from

Nagoya University, Japan in 1980. He was an Assistant Professor at Kyoto

University in 1989. He was an Associate Professor at Nagoya University from

1992 to 1995. Since April 1995, he has been a Professor at Nagoya Univer-

sity in the Department of Engineering. He is currently involved in the study of

high-current interruption phenomena and current limiting technology. He is a

member of IEEE and a member of the Institute of Electrical Engineers of Japan.

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