Impact of a Direct-drive Permanent Magnet Generator (DDPMG) Wind Turbine System on Power System Oscillations

8/13/2019 Impact of a Direct-drive Permanent Magnet Generator (DDPMG) Wind Turbine System on Power System Oscillations

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Abstract--The increase of the large scale wind power

integration have affected many aspects of power systems

operation and behaviors. This paper focuses on the impact of a

grid-connected direct-drive permanent magnet generator

(DDPMG) wind turbine system on damping of power systems

oscillations. In this paper, a detailed model of a DDPMG with

controllers which is suitable for the small signal stability analysis

is presented. The state-space equations of a two-machine system

have been derived to illustrate the mode decouple characteristicbetween a DDPMG wind system and power system and the

insight meaning of this decouple concept has been clarified by

theoretical analysis. The modal analysis technique has been

adopted to reveal the inherent damping characteristics of a

DDPMG wind turbine system and the impact of system

parameters on stability, thereby to confirm the conclusions of the

theoretical analysis. The work can also offer the information for

improving the stability of the system effectively.

Index Terms-- Power system oscillations, Wind power

integration, Direct-drive permanent magnet generator wind

turbine (DDPMG), Small signal stability, Modal analysis.

I. INTRODUCTION

ITH the rapid development in installed capacity of wind

power, the role of wind power on power system

operation becomes more and more important. To some extent,

it changes the structure and the operation mode of the

conventional power system. Therefore the impact of large

scale wind power on power system should be studied.

As one of the major contributors to the increased usage of

wind power, Chinas wind power industry has experienced an

unprecedented growth in recent years. Because of the uneven

geographic distribution between the wind source and the

consumption, Chinas wind power has its own characteristics

which differ greatly from the European wind power such as

concentrated generation and large-scale, long distance

This work was supported by National Natural Science Foundation of

China (50937002) and by the Fundamental Research Funds for the Central

Universities (SWJTU09ZT10)

J. Tan is with the school of Electrical Engineering, Southwest JiaotongUniversity,Chengdu 610031,China.(e-mail:[email protected])

X. Wang is with the school of Electrical Engineering, Southwest Jiaotong

University,Chengdu 610031,China.(e-mail: [email protected])

Z. Chen is with the Department of Energy Technology, Aalborg

University,Aalborg DK-9220,Denmark([email protected])

M. Li is with the school of Electrical Engineering, Southwest JiaotongUniversity,Chengdu 610031,China.(e-mail:qingxiaoyanyuzhong @126.com)

transmission. The effect of wind farms on power system small

signal stability including the influence on damping of the

power system oscillations has attracted more attention, in

particularly, for a large and weakly connected grid such as

China grid. Especially, as the wind power penetration level

and capacity increases, it should be studied further to ensure

the grid operation safety with large scale wind power

integration.

System damping is an important index to evaluate the smallsignal stability of the power systems. In a traditional power

system, the damping is mostly related to the power flow, the

system structure, the generators parameters and so on[1].When

wind power is integrated into a power system, it may affect

the system damping in the following aspects[2-3]: displacing

synchronous machines thereby affecting the electromechanical

modes; impacting major power flows; displacing synchronous

machines that have power system stabilizers; the control

interacting with the damping torque on nearby large

synchronous generators.

The studies of impact of wind power on small signal

stability of the power system are mainly related to two

aspects: (1) The impact on the damping and electromechanical

mode of power system with wind power integration.(2) the

design of wind turbine damping controller to improve the

damping of the system.

Several papers presented some preliminary analysis results.

In 2003, Slootweg initiated the issue about the impact of wind

turbine on power system small signal stability [4], since then

more attentions have been paid to this subject. The common

view is that the fixed speed wind turbine tends to improve the

damping of the system. However, the impact of the doubly fed

induction generators wind turbines (DFIG) and direct-drive

permanent magnet synchronous generator wind turbines

(DDPMG) on power system damping depends on thelocations, integration capacity, control method and other

factors. According to the present research results, the views

about the impact of variable speed wind turbine on power

system damping are controversial and this requires more

investigations.

DDPMG is one of the most potential wind turbine types

because of high efficiency, gearless, low maintain cost, low

noise and etc. [5]. So far, there is not so much research about

the impact of DDPMG on power system damping .The Nordic

Grid has been studied to show that DDPMG decreases the

Impact of a Direct-drive Permanent Magnet

Generator (DDPMG) Wind Turbine System on

Power System OscillationsJin Tan, Xiaoru Wang,Senior Member,IEEE, Zhe Chen, Senior Member,IEEEand Ming Li

W

978-1-4673-2729-9/12/$31.00 2012 IEEE


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damping of the inter-area oscillations slightly[6],while in this

study the DDPMG is modeled as a load, the dynamic

characteristic of DDPMG hasnt been considered. Some

simulation results show that DDPMG based wind power plant

is hard to participate in the system oscillation mode [7-8].

So far, all the research shows that DDPMG has few

impacts on the system damping while the damping can be

improved by an ancillary controller of the DDPMG wind

turbines [9]. The most of the studies are based on the timedomain simulation and modal analysis of a specific case. No

detailed theoretical analyses have been presented to identify

the essence of the problem which still needs a further

investigation.

In this paper, the mechanism of the impact of DDPMG on

power system damping has been represented. The paper

organized as follows: Firstly, a basic mathematic model of the

wind turbine with DDPMG which is suitable for small signal

stability studies are presented. Then the state space equations

of a two machine system have been derived. The mode

decouple characteristic between the DDPMG and the grid has

been proved and highlighted. After that, the base

characteristics of a study case have been studied by modalanalysis, and the effect of different parameters of the wind

turbine and controllers have been studied in detail. Finally, the

conclusions are drawn. In this paper, theoretical analysis

provides an insight and a better understanding of the basic

properties of the impact of DDPMG on damping of power

system.

II. THE SMALL SIGNAL MODELING

Small signal stability is the ability of the power system tomaintain synchronism when suffering small disturbances. It

only needs to concern about the dynamic phenomena of the

power system in a frequency range of 0.1Hz to 10Hz. It isnecessary to develop the appropriate model for wind turbine

for the analysis of small signal stability to concentrate on the

study subject. In this situation, network transient and higher

harmonics can be neglected. Only the fundamental frequencycomponent should be presented.

A typical structure of a variable speed wind turbine with

DDPMG is depicted in Fig. 1. The wind turbine model

includes aerodynamics model, drive train model, generatormodel, converters model and controller model. Limiters and

protective circuits are not modeled here since they dont affect

small signal stability when the system is suffering a small

disturbance and the voltage and frequency are within their

boundary values. For the sake of completeness of the paper,the modeling parts are introduced in brief as following.

A. Aerodynamic model

At a specific operation point, the mechanical power is

considered as constant which means the wind speed and thepitch angle dont change during the period of study. A

simplified aerodynamic representation is

= 0.5

(,) (1)

Where Pis power extracted by the turbine from the windis air densityRis the blade radiusCis theaerodynamic efficiency of the rotoris the tip speed ratiois the pitch angleVis the wind speed.B. Drive train model

The shaft of conventional synchronous generators is

normally neglected in power system dynamics stabilitysimulations, because the torsional resonance frequency is

above 10 Hz which is out of the upper limit of the investigated

frequency band. However, in the wind turbine system, due to

the softness of the low speed shaft, its resonance frequency isaround 2 Hz and the shaft model must be taken into account.

A two-mass model representation of the drive train is proper

to illustrate the dynamic impact of wind turbine on the grid

[10].The representation of two-mass model is

= ( ) (2) = + ( ) (3)

= (4)

Where is moment inertial of the wind turbine, ismoment inertial of the generator, Kis stiffness coefficient, D

is damping coefficient, is speed of turbine, is speed ofgenerator shaft, is the angular displacement between the

two ends of the shaft. Here, all the quantities are expressed inSI unit.

C. Generator

The model of the permanent magnet synchronous generator

is based on the following assumptions: magnetic saturation isneglected, flux distribution is sinusoidal, and all losses are

neglected, except for copper losses.

In most of the stability studies, usually the stator transient

can be neglected.The stator voltage equations of the generatorcan be simplified as

= (5)= + (6)

Where,are the terminal stator voltage, i,are thestator currents,and are the stator inductances in the dqreference frame, is the magnitude of the flux induced in thestator by the permanent magnets on the rotor, is theelectrical speed.

For a non-salient-pole machine, the inductance and are approximately equal. Assuming L = L , the electricaltorque of the generator can be expressed by

= 1.5 (7)Where T is the electrical torque and p is the pole pair

number.

Fig. 1. Structure of a variable speed wind turbine with DDPMG


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D. Converter and DC link

The full-scale frequency converter in a wind turbine withDDPMG consists of a generator-side converter and the grid-

side converter connected back to back via a dc-link. For a

detailed PWM voltage-source converter model, the switchfrequency of the power electronic components is quite high.

However, the converter can be modeled as an average model

without considering switch dynamics which is out of the

interested frequency band[11]. The average model is based onthe energy conservation principle. The instantaneous power of

ac side of converter is equal to the dc side ignoring the power

loss. Assuming the converter is lossless, the active power

balance equations as follows,

= (8)Where is the active power from the stator of generator,is the active power through the DC-link capacitor and

is the active power to the grid. The dynamic expressions of dc-

link can be derived as follows,

= + (9)Where C is the capacitance of the capacitor, vandvare

the terminal voltage of the gird side converter,

iand

iare

the current of grid.

E. Controllers

This section describes the control strategies and the model

of controller for the DDPMG system. The control strategiesused in this study is based on the idea that the generator-side

converter controls the rotor speed to maintain the optimal tip

speed ratio and minimize the power losses in the generator,while the grid-side converter control DC-link voltage constant

and reactive power flow to the grid[12]. Normally, the

reference value of the grid-side reactive power is set to zero tomake sure that the power factor of the grid side is one. All the

controllers are PI controllers.

The control scheme can be expressed by a set of differentialand algebraic equations as follows:

= _ (10) = (11)

= + (12)

= _ + + (13)= + + + (14)

= _ (15)

= _ + (16)

= _ (17)

= _ + + (18)

= _ + (19)

Where K ,, K and K ,, K are proportional andintegrating gains parameters of six PI controllers,x,,xareintermediate variables.

F. Smooth filter

The inductive filter is designed to limit harmonic currentinjection into the grid. The dynamic equations are as follows:

= +

(20)

= +

(21)

Where, Ris the resistance of the filter and Xis the reactanceof the filter.

III. MODE DECOUPLE ANALYSIS

A. Study system description

To investigate the impact of wind power on power systems

oscillations, two-machine system has been developed for this

study. The schematic representation is depicted in Fig. 2. Thewind turbine system connected to the power system via a

transmission line. The grid is modeled as a synchronous

generator. The load is modeled as a constant power load. Thisstudy system can show the oscillation relationship between the

synchronous generator and wind turbines and is useful for

parametric studies.

The DDPMG wind turbine system is modeled as a 12 ordermodel as described above. The synchronous generator adopt

classical two order model. It can be expressed as

= (22)

= (23)Where Jis moment inertial of the synchronous generator, is angular velocity, is the angular position, T is

mechanical torque,Tis electromagnetic torque.The Network voltage equation in x-y frame can be

expressed as

= (24)Where V and V are magnitudes of voltage and , are

angular of the voltage, X is the reactance of thetransmission line, is the current.

B. System state-space representation

For analysis of power system dynamic performance, thecomponent models are expressed in the state-space form. The

DDPMG system with controllers can be represented by a setof differential equations (2)-(4),(9),(10)-(21) and algebraicequations(13),(14),(18),(19). The network equations (24) can

be rewrite in d-q frame as

z= g(u) (25)Where z are the voltage variables and u are current

variables of the network.The state variables, output variables and input variables are

chosen respectively like followingx = [w, w, , x, x, x, v, x, x, x, I, I, , ] (26)

z = [V, V, V, V] (27)

Fig. 2. Structure of a two-machine system


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u = [V, V, I, I] (28)Combining the equations (22), (23) and differential

equations of DDPMG system forms the differential equationsof the whole system

x = f(x,u,z) (29)The algebraic equations of WT system can be written as

z = g(x, u) (30)Combining the equations (5), (6) and (25) forms the

network extended equations to keep consist with the order ofoutput matrix as following

z = g(u) (31)Equations (29)(30)(31) are linearized at an equilibrium

point which is the steady state operating point. Therefore, the

linearized forms of equations are as follows

= + + (32) = + (33)

= (34)Where A, B, C, D, E, F are parameter matrixes.

By taking equation (33) and (34) into equation (32), the

small signal model of the wind turbine with DDPMG

connected with a synchronous generator can be derived as

= (35)= + + ( ) (36)

is referred as characteristic matrix. Analysis of theeigenproperties of provides important informationregarding the stability characteristic of the system.

C. Decouple analysis

The state-space representation of the two-machine system

can be derived from the equation (36) as the following form:

=

(37)

Where kij (i=114, j=114) is the parameter of thecharacteristic matrix. They are related to the parameters of the

system and the initial states of the variables. The first six state

variables are generator side state variables and the seventh

variables is a dc-link state variable and other state variables

are grid side state variables.From the equation (37), we can see that there is no cross-

coupling between the generator side state variables and grid

side state variables which mean the change of the generatorside state variables can hardly affect the grid side state

variables, vice versa.

The seventh row ofmatrix shows that the dc-link is theonly link between the generator side state variables and grid

side state variables. Although the generator side state variables

hardly affect the grid side state variables directly, they canaffect the dc-link and thereby affect grid side state variables

indirectly, the link is the active power transmission.

One of the goals of the controller is to maintain the voltage

of DC-link constant. During a small disturbance, assume

V=0 and the dynamic of the dc-link can be ignored. Thestate-space representation of the system can be simplified asthe following form:

= (38)Where A is a parameter matrix of size 66 B is a

parameter matrix of size 77The characteristic equations

of A can be expressed as two parts ()= ()() (39)

Where, is the eigenvalue of A , f is the characteristicequations.

A and B are two isolate parameters matrixes. Theparameters in A are only related to the generator sideparameters which include the parameters of the wind turbine,

the generator, initial value of the state variables, inputvariables and output variables and the generator side controller.

The parameters in B are only related to the grid sideparameters which include the grid side converter controller,

transmission line and the synchronous machine.

From the structure of A , it can be seen that theeigenvalues of the whole system comprise by two isolate parts.

One is depended on generator side parameters and the otherone is depended on grid side parameters. That means the

change of the wind turbine parameters and generator side

controllers parameters can hardly change the grid sideoscillation mode, vice versa.

That is to say, the change of state variables and parameters

of the generator side can not affect the eigenvalue of the gird

side, thereby generator side components cant participate the

grid side modes.Further, the dynamic characteristics of the generator side

components cant affect intrinsic oscillation modes of the

power system, not to mention the electromechanical

oscillation mode of the power system.The generator side components of wind turbine based on

DDPMG doesnt bring any new mode to the system oscillation

mode while the voltage of dc-link keeps constant. A grid sideconverter controller may have some effects to the power

system damping. Parameter kkkk arerelated to the controller parameters of the grid side converters.

They are able to have the impact on state variables of thesynchronous generator.

In this paper, the control strategy is described in part IIsection E. This conclusion is related to the control strategies.More control strategies need to be investigated further.

IV. VALIDATIONANDRESULTS

A. Case Study

The two machine system is adopted in this study as

described in Fig.2. The input mechanical power is assumed

constant. This assumption is good to observe the inherent

mode of the wind turbine system at one specific operation

point. In this study, the wind speed is at the rated wind speed,


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10m/s. The detailed parameters of the system can be found inappendix. The eigenvalues are solved by the characteristic

equations (37).The eigenproperties of this system are shown in

Table I.TABLE I

MODE OF THE STUDY CASE(A)EIGENVALUE AND MODES OF TWO MACHINE SYSTEM

Mode Eigenvalue Mode

1.1055 10 Generator side

3.1338 10 Generator side

, 6.33 101.39 10i Grid side, 4.6510 2.90 10i Grid side, 3.861610 4.3684i Shaft oscillation, 2.2010 1.27 10i Grid side 1.06210 Generator side 1.02210 Generator side

, 1.7085 1.511910i SG

(B)OSCILLATION FREQUENCY,DAMPING RATIO OF OSCILLATION MODES

(C)PARTICIPATION FACTOR OF OSCILLATION MODES

The eigenvalue and the type of the modes are shown in

Table I (A), oscillation frequency, damping ratio of oscillationmodes are shown in Table I (B) and participation factor of

oscillation are shown in Table I (C).This system is stable since all the eigenvalues have the

negative real part. There are 14 modes existing in this systemincluding five oscillating modes. From the participation

factors, the dominate states can be found out. They also show

the physical nature of the modes:

(1) , are non-oscillating modes associated with thedynamic of the drive-train model .They are related to the

mechanical part. , is the shaft oscillation mode whichfrequency is 0.69Hz. It is in the range of the interested

oscillation frequency. The damping ratio of this mode is 0.08which is close to the critical damping, so this mode should be

paid attention to.

(2), ,, and , are electrical oscillation modesassociated with the dynamics of DC-link and grid side current.The oscillation frequencies are respectively 22.189Hz,

4.6221Hz and 2.0228Hz. These three oscillation modes have

high damping ratios which mean these three oscillations have

been well damped.

(3) and are stator modes. Since in this model, thedynamics of stator has been neglected reasonably, it is

reasonable to see that the stator oscillation mode cannot be

represented in this system.

(4), is the electromechanical oscillation mode of thesynchronous generator From the participation factor we can

see that the wind turbine system doesnt participate in theelectromechanical oscillation mode at all. The damping ratio is

low because of the adopted classical two order model without

considering the damping of the generator.

B. Time domain simulation

The two-machine system model is set up in

PSCAD/EMTDC to verify the oscillation modes.

A step change of wind speed from 10m/s to 9m/s at 12s is

taken as the small disturbance. The time domain response ofthe active power of the transmission line is shown in Fig.3.

Fig. 3. DDPMG mode in time domain: response of transmission lines active

power with a step change of wind speed

The total least square estimation of signal parameters via

rotational invariance techniques (TLS-ESPRIT) algorithm hasbeen proved efficient and good noise immunity in low

frequency oscillation analysis [13]. It is adopted here to

analyze the oscillation frequency of the time response signal,

the result is shown as Table II.TABLEII

MODE ANALYSIS BY TLS-ESPRIT

Mode Frequency(Hz) attenuation amplifier

1,2 0.6697 0.52 0.93013,4 1.9327 2.03 0.0062

The frequency of dominant oscillation modes is 0.670Hz,

which is close to the frequency of the shaft mode ,. Themode 3, 4 with a frequency 1.933Hz which is close to mode

, can be visualized with a quite low participation. Thesynchronous generator oscillation mode can be visualized in

the starting period with a measured frequency, 2.3Hz.However, the change of the wind speed cant excite the SG

mode with appearing in active power oscillation. In some

extent, the modal analysis result has an agreement with the

time domain analysis result.From the result of time domain simulation, the shaft mode

still can be visualized in gird side power since the voltage of

DC-link is hard to keep completely constant during the

disturbance. If the voltage can be controlled as a constant, the

generator side subsystem is totally decoupled with the gridside subsystem as above theoretical analysis.

Since the structure and parameters of the generator side

component cant affect grid side mode. Only generator sidedynamic characteristic should be considered from the view of

grid side. Oscillation mode may be presented in the form of

active power oscillation which can be treated as an input to thegird side.

As above discussion, the impact of DDPMG wind turbine

on power system stability can be classified into two parts: the

grid side controller and the active power input. Although this

Mode frequency Damping ratio

, 22.189 0.97, 4.6221 0.84, 0.6953 0.08

, 2.0228 0.86

, 2.4062 0.11

Mode , 0.2 0.4 0.2, 0.2 0.2 0.3 0.3, .5 .5, 0.2 0.4 0.2 0.2, 0.5 0.5


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choose the value of the reactance, we should notice that higherinductance of the filter leads to lower current total harmonic

distortion (THD) values [12].Considering the stability issue,

the choice of LI should be compromised.

In addition, from above study results, we can see that theparameters of generator side such as inertia, damping

coefficient, stiffness cant affect the grid side mode. In like

manner, the parameters of the grid side, such as LI, cantaffect the generator side mode. It proves that the grid side

mode and the generator side mode are decoupled.

D. Effect of grid strength

Grid strength is an important indicator to study the stability

of the power system. Reactance of the transmission line can

express the line strength (weak connected or strong connected)

in a specific system. A longer transmission line has a higher

reactance.

Fig. 8. Root locus for increasing line reactance

Fig.8 shows the corresponding eigenvalue displacement

while Xlineincreases from 0.008 ohm to 0.16 ohm. Reactance

Xlineonly affect four oscillation modes of grid side including

the synchronous generator mode. Most of the oscillation

modes move toward right as X lineincreases. That means with

the increasing of line reactance, the system has a trend to be

unstable. The mode , strongly related to grid side currentmoves into a critical region which damping ratio less than 0.05when Xline reaches 0.09. And mode ,which is related tosynchronous generator moves to right.

F. Effect of controller parameters

In the wind turbine system, the parameters of the controllerare very important. Improper parameter may cause instability

of the system. Here, we choose the controllers parameters

based on reference [11] as the typical values.Kp1-Kp3, Ki1-Ki3 are PI parameters of generator side

converter and Kp4-Kp6, Ki4-Ki6 are PI parameters of grid side

converter. The effect of each parameter should be studied

individually while other parameters should be kept as the

typical values. The method is the same as the above case study.For the limited space, the result has been organized in the

Table III and Table IV to show the corresponding varying

eigenvalues and their dominant states.

From the Table III, it can be seen that Kp1-Kp3, Ki1-Ki3are

only related to state variables of the generator side converter

and the shaft. From the Table IV, it can be seen that Kp4-Kp6,

Ki4-Ki6are only related to grid side converter and DC-link. It

proves varying the parameter of the generator side controller

cant affect the state variables which are controlled by grid

side converter, vice versa.

It should be noticed that neither grid side controller norgenerator side controller can control the shaft oscillation mode,

so an accessional controller should be added to damp this kind

of oscillation mode.TABLE.III

THE EFFECT OF CHANGING PIPARAMETERS OF THE STATOR SIDE CONVERTER

PI parameters mode Dominant state variables

Kp1Ki1 Mechanical speed ofwind turbine

Generator sideelectrical quantity

Kp2 Ki2

Kp3Ki3

TABLE IV

THE EFFECT OF CHANGING PIPARAMETERS OF THE GRID SIDE CONVERTER

PI

Parameters

mode Dominant state variables

Kp4,Kp5,Kp6

Ki4, Ki5, Ki6

, I, I DC-LinkGrid side

converter XX,X

I, I X, I,X, I

V. CONCLUSION

This paper presented the theoretical analysis of mode

decouple characteristic of a DDPMG wind turbine system. Atwo machine system is adopted to study the impact of

DDPMG wind turbine system on damping of the power

system oscillations.It illuminates that the change of generator side state

variables and parameters cant affect the grid side mode, viceversa. Grid side mode and generator side mode are decoupled

and isolated. Generator side dynamic component can not

affect grid side mode or bring the new electromechanical

mode.

Modal analysis method is adopted to analyze the impact ofthe wind turbine parameters, the controller parameters and

transmission line parameters on system modes, which is used

to confirm the theoretical analysis. This also helps tounderstand the nature oscillation mode of the system.

It should be noticed that since the basic PI controller cant

control the shaft oscillation mode, it is necessary to design an

accessorial controller to damp this mode.The impact of DDPMG wind turbine on power system

stability can be classified into two parts: the grid side

controller and the active power input. The generator side mode

such as shaft oscillation mode can be visualized in grid side inthe form of active power and the affect the grid indirectly.

This paper using linear techniques provides information

about the inherent dynamic characteristic of the power system

and the information may be used to assists in controller design

in the future.

VI. APPENDIX

A. Parameters of the PMSG wind turbine

Rated power=2MW;

Rated voltage=0.69kV;

Rated speed=15.5r/min

Wind turbine rotor radius=40m;

Wind turbine inertia=5s;

Generator inertia=0.5s

Wind speed=10m/s;


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Reactance of stator = 2.610;Resistance of stator=0.9510;Pair pole=58;

Flux linkage=4.6Wb;

Voltage of DC-LINK=1.1kV;Smooth inductance=0.0014H;

Smooth resistance=0.0058;B. Parameters of the synchronous generator

Power of the load=4MW;Inductance of transmission line=0.149H;

Inertia constant= 1.95s;

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[13] P. Tripathy, S. C. Srivastava and S. N. Singh, "A Modified TLS-ESPRIT-Based Method for Low-Frequency Mode Identification in

Power Systems Utilizing Synchrophasor Measurements," IEEE Trans.

Power System, vol.26, pp. 719-727, 2011.[14] Z. Lubosny, Wind Turbine Operation in Electric Power Systems:

Advanced Modeling, Berlin: Springer, 2003,p87-94.

Jin Tan received B.Eng. degrees in electrical engineering from Southwest

Jiaotong University, Chengdu, China, in 2007.

She was a visiting student in the Department of

Energy Technology, Aalborg University, Aalborg,

Denmark for two years. She is currently a Ph.D.candidate in Southwest Jiaotong University. Her

current research interests include integration of

PMSG based wind generation system and power

system stability and control.

Xiaoru Wang (M02

SM07) received a B.Sc.

degree and a M.Sc. degree from Chongqing

University, China, in 1983 and in1988respectively, and a Ph.D. degree from

Southwest Jiaotong University, China, in 1998.

Since 2002, she has been a Professor in the

School of Electrical Engineering, SouthwestJiaotong University. Her research interests lie in

the areas of power systems protection and

emergency control. Since 2009, she has extended her research to modern

power system with a large scale renewable power penetration.

Zhe Chen(M95SM98) received the B.Eng. andM.Sc. degrees from Northeast China Institute of

Electric Power Engineering, Jilin City, China, and

the Ph.D. degree from University of Durham, U.K.

Dr Chen is a full Professor with the Department of

Energy Technology, Aalborg University, Denmark.

He is the leader of Wind Power System Researchprogram at the Department of Energy Technology,

Aalborg University and the Danish Principle

Investigator for Wind Energy of Sino-Danish

Centre for Education and Research.

His research areas are power systems, power electronics and electric

machines; and his main current research interests are wind energy and modern

power systems. He has more than 260 publications in his technical field.

Dr Chen is an Associate Editor (Renewable Energy) of the IEEE Transactions

on Power Electronics, a Fellow of the Institution of Engineering andTechnology (London, U.K.), and a Chartered Engineer in the U.K.

Ming Li received B.Eng. degrees in electrical engineering and automation

from Zhengzhou University of Light Industry, Zhengzhou, China, in 2004.He is currently a Ph.D. candidate in Southwest

Jiaotong University. He current research interests

are power system interharmonics analysis andsignal processing technology.

Documents

Impact of a Direct-drive Permanent Magnet Generator (DDPMG) Wind Turbine System on Power System Oscillations