review on frequency control of power systems with wind power penetration51

7/27/2019 Review on Frequency Control of Power Systems With Wind Power Penetration51

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Review on Frequency Control of PowerSystems with Wind Power Penetration

Yuanzhang , mb EEE Zhaui ZHANG, Gujie LI, mb EEE and in LIN

Abstract-The ineing peneion of wind powe myinuene he fequeny iliy of powe yem. Theefoe,new onol heme e neey fo wind uine nd poweyem o uppo he fequeny onol. Cuenly, mo of hepulihed onol mehod n e lied ino 3 level, i.e.,

wind uine level, wind fm level nd powe yem level. Thewind uine level onol enle wind uine, piully hevile peed wind geneo, o povide dynmi epone ndpowe eeve fo he pimy fequeny onol yimplemening he ineil, doop o deloding onolle. Thewind fm level onol diiue he enl onol ommndfom he yem o he lol wind uine nd enegy ogeuni fo he deied geneion. The powe yem level onoloodine wind fm wih onvenionl powe pln fo heeondy onol o eove he fequeny o he efeene vluefe hn fo he no oodinion onol e. Thi ppepeen eview on he le udie in elion o he 3levelfequeny onol of powe yem wih wind powe peneion.

d rs-Cenl onol, oodinion onol,deloding onol, doop onol, fequeny onol, ineilonol, lol onol, powe yem, wind fm, wind uine

I. NTRODUCTON

IN recent years, power systems are facing more equencystabili challenges with large-scale wind power integrating

into the grid. Synchronous generators can automatically

regulate the speed governors to support frequency control.

However, wind generators provide small or even no

contributions to equency stabili. Therefore, the equency

control schemes are required to be well designed for the

system with wind power to maintain the equency deviating

inside the appropriate region.

For a equency drop event, three securi indices, i.e.,

equency change rate, equency nadir ad steady stateequency deviation [1][2] and their impact factors are taken

into account in this paper. The equency change rate is

determined by the inertia of the whole system; The equency

nadir is determined by the power disturbance, the kinetic

energy of the rotating masses, the number of generators

subjected to prima control and the dynamic characteristics

of the generators, loads and controllers; The steady state

equency deviation is determined by the droop characteristics

This work was supportd in part by National Natural Scinc Foundationof China (50977050)

Th authors ar om Stat K Laborato of Powr Sstms, Dpartmntof Elctrical Enginring,Tsinghua Univrsity, Bijing 100084, P China

(-mail: zhangzs05@mailstsinghuaducn).

978597/ /$6 EEE

of all generators. Chinese standard [3] requires the maximum

equency excursion of 0.2 Hz. This excursion can berelaxed to 0.5 Hz if the system capaci is small.

The equency control of power systems is usually formed

of prima control and seconda control [1][4]-[7]. The

primary control is an automatic adjustment of power by thelocal control and inerial response of the generators and loads

within 30 seconds [4][5]. The instantaneous power and power

consumption are balanced so the equency is re-established

by the primary control aer a equency event. However, the

re-established equency is usually dierent om the

reference value. In the secondary control, the speed droop

characteristics of the generators are increased or decreased by

the operators or automatic generation control (AG).

Therefore, the equency can be reset to the reference value

om 30 seconds to 30 minutes aer a equency event [4].

This paper presents a review on the participation of wind

power for the prima and seconda equency control.

According to the latest studies, the control schemes can bedivided into a 3-level hierarchy, i.e., wind turbine, wind farm

and power system level controls. On the rst wind turbinelevel for the prima control, the additional local controllers

including inertial, droop and deloading controllers are

installed on the power electronic converers of variable speed

wind turbines or the pitch controllers of all kinds of wind

turbines. The inertial control supports the equency control in

the transient process. The droop control simulates the similar

equency droop characteristics to that of synchronous

generators. The deloading control provides the power reserves

for the wind farm. On the second wind farm level, the desired

generation for the system is achieved in the cooperation of

central control and local control. The central controller

receives the power command om system operators or AGC,and then distributes this command to the local controllers of

the wind turbines ad energy storage units in the wind farm.

On the third power system level for the seconda control, a

better equency behavior is obtained by the coordination

control between the AGC-controlled thermal plants and the

wind farms. The thermal plants can be started earlier by the

coordination controller to support the equency control and

the equency can be recovered to 50 H faster than for the nocoordination case.

II.ND RBNE EVEL ONTROL

Wind turbines can be divided into xed speed and variable

speed categories. A xed speed wind turbine generally utilizes


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a turbine, a gearbox and a squirrel-cage induction generator to

convert the mechanical energy into electrical energy. With a

low normal slip of 1%-2% [8], a xed speed wind turbine can

provide an inertial response to the equency uctuation due

to the coupling between the rotational speed and system

equency. Thus, the integration of xed speed wind turbinesincreases the system inertia, however, the inertial response is

generally smaller and slower than that of synchronous

generators [8][9].

Variable speed wind turbines mainly refer to permanent

magnet synchronous generators (PMSGs) and doubly fed

induction generators (DFIGs). A PMSG contains a multi-pole

magnet rotor and a back-to-back ACDCAC converter

attached to the stator. Consequently the generator is fully

decoupled om the grid. The energy is transmitted through

the converter om the stator to the grid. DFIGs that are more

common than the other wind turbine technologies also use

power electronic converters, however, attached to the rotors.The rotor that supplies the AC excitation current is connected

to the power system through the converter while the stator is

connected directly to the power system [10].

The power electronic converters enable the variable speed

wind turbines to capture wind energy over a wide range of

wind speeds, improve the power quali and regulate both the

active and reactive power. However, the decoupling control

isolates the rotational speed om the system frequency so the

variable speed wind turbines oer no response to the

equency excursion [8]. Another problem is that traditional

wind turbines always operate at the maximum power point

tracking (MPPT) so they store no power reserves to support

the equency control in the steady state.In the wind turbine level control, additional controllers are

installed on the converters of variable speed wind turbines or

pitch controllers to relate the electromagnetic torque andequency. The wind turbines transiently support the

equency control by implementing the inertial control which

is obtained by the approaches of "hidden inertia emulation

and fast power reserve emulation. The droop control simulates

the similar equency droop characteristics to that of

synchronous generators. The deloading control enables the

wind turbines to operate over deloading curves instead of the

MPPT and saves the available power as reserves by using

pitch control (pitching) or increasing the rotational speed fromthe MPPT value (overspeeding). The power reserves can

balance the instantaneous power and provide the permanent

support for the long-term frequency regulation. Therefore,wind generators are able to participate in the primary

equency control by using the wind turbine level control

A Inertial Control

(a) "Hidden inertia emulationThe basic reason for emulating the "hidden inertia is to

reduce the maximum equency change rate [11].

Synchronous generators and xed speed wind turbines can

automatically release the kinetic energy of the rotating mass

for a sudden equency change while variable speed wind

2

turbines cannot due to the decoupling operation [12].

However, a variable speed wind turbine can emulate the

similar inertia to that of synchronous generators by

implementing the inertial controller as shown in Fig. 1 [13].

P MT Pre f 1-- --- :f-" ____

Fig. I. "Hiddn inrtia mulation for variabl spd wind turbins.

The inertia constant is always used to express the inertial

characteristics. The so-called "hidden inertia of variable

speed wind turbines is estimated by [12][14]:

JOom2

(1)

where S is the nominal apparent power, Onom is the nominalrotor rotational speed and J is the equivalent moment of

inertia. The "hidden inertia is comparable to the inertia of

conventional generators [15]. For a two-mass mechanical

model used in this work, Jis [10][16]:J Jlr n2 +Jgen (2)

where n is the gearbox ratio, .r is the turbine moment ofinertia and Jgen is the generator moment of inertia. For a 2 MWwind turbine, the total moment of inertia is approximately six

times of that of the conventional generator [17]. The active

power control signal (inertial power) Pin of the inertial controlis achieved by [12][14]:

dsysn 2 x sysxdt

where Osysis the system rotational speed.

(3)

The wind turbine can fast store or release a large amount of

kinetic energy in the rotating mass because of the power

electronic converter control, large moment of inertia and wide

rotational speed range. Variable speed wind turbines can

considerably release greater kinetic energy than xed speed

wind turbines and conventional generators can [12][15].

Fast power reserve emulation

In fact, the inertial power is just a control signal and it canbe dened in dierent forms om (3) For example [5]

dened the inertial power as a constant power of 10% nominal

active power for 10 seconds over a wide operation range for

an E-82 2 MW wind energy converter. The short-term

constant power which is called "fast power reserve can

support the equency control for a short while [15][18][19].

The fast power reserve Potis derived om [18]:1 2 1 2ons'! 'JOro -'JOrt (4)

where t (t < tm is the lasting time of the fast power reservesince the beginning of the equency event, O is the initialrotor rotational speed and O is the rotor rotational speedcorresponding to t Thereby the reference rotor rotational


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speed in Fig. 2 is obtained by:

.-{r,re/ ={ = rO2 2 C;f

!

(5)

v :

Fig. 2. Fast pr rsrv mulatin fr variabl spd ind turbins.

The fast power reserves compensate the power loss for a

short period and save time for other slower generators to

participate in the equency control [18].

B. Droop Control

The droop control is described by the equency droop

characteristics in Fig. 3 [20] to produce an active poweroutput change which is proportional to the equency

deviation [14][21][22]. The equency deviation is given by:

=Ime - Jom (6)where Imeas is the measured system equency and fom is thenominal system equency (reference equency). The active

power control signal (active power increase) of droop control

is obtained by:

M=P= (7)

wwhere R is the speed adjustment rate, P is the total activepower corresponding to Imeas and is the initial total active

power corresponding tofom.

m

Fig. 3. Frquncy drp charactristics.

One application of droop control is to be implemented in

the converter of variable speed wind turbine as shown in Fig.

4 [14]. However, the power increase P which is absorbed

om the kinetic energy causes the rotational speed decrease

due to the MPPT operation. The turbine may stall if the

rotational speed is falling too low. This phenomenon may not

be avoided because the wind turbine cannot provide extra

permanent power to reduce the equency deviation [9].

Therefore, the droop controller should be ended on time like

the fast power reserve emulation.

--------------------

: D if 1___-i:. l ____________________ J

+

3

P M + Pf II.:I Cv L ____ .

Fig. 4. Drp cntrl fr variabl spd ind turbins.

Another application is to use the droop control with the

deloading control that is presented in Section II-C. Droop

control does not affect much initial equency change rate but

greatly inuences the equency nadir [16].

Deloading ControlTraditional wind turbines always operate on the PT

curve in Fig. 5 to extract the wind energy as much as possible.

The deloading control enables wind turbines to operate overdeloading curves instead of the MPPT and save the available

power as reserves for the long-term equency control. The

deloading possibilities are obtained by pitching and

overspeeding as shown in Fig. 5 [23]-[25]. The active power

can be changed by regulating the pitch angle om {min to alarger value { for a constant wind speed Vw and constantrotational speed. The power can also be changed by increasing

the rotational speed over the MPPT speed for a constant wind

speed Vw and a constant pitch angle {min'

p MT .

Fig. 5. Dlading pssibilitisvrspding and pitching.

In fact, decreasing the rotational speed below the PT

speed (underspeeding) in Fig. 5 is as well as a deloading

possibility. However, underspeeding may decrease the smallsignal stabili while overspeeding improves the small signal

stability compared with pitching [23]. Meanwhile, the rotor

has to rstly absorb extra energy om the grid and increase

the rotational speed which may lead to a second equency

drop. Therefore, overspeeding is preferable [24][25].

(aJ Pitch controlTraditional pitch control is valid when the rotational speed

is above the maximum value for a high wind speed condition

as shown in Fig. 6 [10]. Fig. 7 shows a kind of modied pitch

control which is widely used at present to store power reserves

for wind farms [13][26]-[28].


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x

Fig. 6. Traditional pitch contrl.

Fig. 7. Modid pitch contrl.

The pitch control is feasible for both variable speed and

xed speed wind turbines. The response of pitch control is

slower compared with the system frequency dynamics because

of the mechanical time constant of the pitch controller [11].

) Rotational speed controlOverspeeding is achieved by the rotational speed control in

Fig. 8 which is more convenient than pitch control when the

rotational speed is below the maximum value [11][23]. In

addition, overspeeding can protect the pitch blade om wear

and tear compared with only pitching for the low wind speed

condition [23]. However, the wind speed is difcult to be

accurately measured [25].

Fig. 8. Rotational spd control for variabl spd wind turbins.

Unlike pitch control which involves the servo time constant,

rotational speed control is obtained by the power electronic

converter of the variable speed wind turbine in a considerably

faster manner [11].

D. Discussion

The equency change rate is decreased by the inertial

control during the transient process. The frequency nadir is

increased by inertial control and droop control. The steady

state equency deviation is reduced by the deloading control

[14][21][22][29]. Therefore, the three equency securityindics may b maintaind at th appropriat valus if th

inertial, droop and deloading controllers are applied together.

In the inertial and droop control, the rotational speed rstly

decreases because the kinetic energy is released to the grid.

Therefore, the controllers should be ended on time to prevent

the turbine om stalling by decreasing the rotational speed

below the lower limit.

The loading of generators also aects the dynamic response

of the wind turbines in the MPPT operation. For instance, [16]

showed that DFIG could barely provide the required inertial

response without exceeding the rotor current limit if the

MPPT power were over 80% rated power. At rated power, thedynamic contribution is restricted because the rotor current is

4

already around its maximum value ad it cannot be much

rther increased. Therefore, the deloading control is

necessa not only to keep power reserves but also to improve

the capabili of dynamic response.

III. ND F EVEL ONTROLThe overall model of wind farm level control is built up

with a hierarchical structure of central control and local

control as shown in Fig. 9 [6][30]-[32]. The central controller

receives the active power command PWF om the operators orAGC (secondary control). Aer that, PWF is distributed to thelocal controllers of wind turbines and energy storage system

(ESS) units for the desired generation. The local controller

ensures the distribution signal and sends the feedback

information of generation capabilities to the central controller.

Pwn'" j

MT1Wd fam poe commad distbutio

AESS1

La

Ca

Fig. 9. Wind farm lvl control hirarchcntral control and local contrl.

A Local Control

The local control scheme use either a number of deloaded

wind turbines or ESSs in a wind farm [31][32]. The deloading

control proposed in Section II-C receives the control

command om the wind farm in Figs. 7 and 8 for the

seconda equency control.=GiFig. 10. Distributd ESS and aggrgatd ESS.

There are basically two ESS congurations in a wind farm

as shown in Fig. 10 [32], i.e., (a) one large aggregated ESS

which is directly connected to the grid based on the exteal

and non-wind technologies like batteries, compressed-air and

pumped hydro [33] for the whole wind farm and (b) several


5/8

small distributed ESSs which are installed on the variable

speed wind turbines by implementing the devices such as

baeries [34], ywheels [35] and supercapacitors [36]. The

distributed ESS on PMSG is similar to that on DFIG in Fig.

10 and is also connected to the DC part of the ACDCAC

converter. [32] showed that the distributed ESS was aseective as the aggregated ESS in frequency deviation

reduction.

The choice of ESS depends on the demands of the control

process. From the point of view of reaction time, there are fast

and slow energy storage devices. From the point of view of

capacity, i.e., the length of operating time, there are short-,

medium- and long-term energy storage devices. For equency

control, fast and medium-term ESS is suitable [31].

B. Central Control

The set point PWF of system command should beappropriately allocated to wind turbines and ESS units by the

wind farm central control as follows:

P =PTlola + PSlola (8)where Ptta! is the total active power command for the wind

turbines and PESStta! is the total active power command for theESS units. The simplest distribution scheme is based on

equitable distribution, thus the output control signal for the i

th wind turbine is obtained by [6]:

- PMTii - tota nLPMi=

(9)

where PMTiis the generation ability (MPPT power) of the ith wind turbine corresponding to the wind speed. Similarly,

the output control signal for the j-th ESS is:

AEESjP =PSlola -k

LAEjj=1

where AESSj is the capacity of the j-th ESS.

(10)

[37] described another rough distribution method to restrain

the power uctuation which was caused by the random wind

speed. In short, the higher the wind speed is, the larger the

weighting factor for the wind power output is. Therefore, the

output control signal for the i-th wind turbine under wind

speed Vw is given by:

= .W(Vw)xN(Vw)

._1_i lola LW(Vw)xN(Vw) N(Vw) (11)where (Vw) is the number of wind turbines operating at windspeed Vw and W(Vw) is the weighting factor for each level ofwind speed, e.g., assuming that the wind speed range is 15ms in the wind farm, separate the range into 5 levels and

dene 11 ms = , 112 s = 2, ..., 415 ms= 5. Therefore, the wind turbine under higher wind speed is

roughly assessed to provide more power than the wind turbine

under lower wind speed. The wind speed uctuation is not

considered any rther in this paper.

. Discussion

As mentioned in Section II-B and D, the inertial control or

5

droop control should be ended on time to prevent the

rotational speed om falling too low. However, there will be asudden drop of the power output when switching o the

controller. The undesirable sudden drop may cause another

equency reduction especially when many generators end the

controllers together. The solution is to switch o eachcontroller at different time or by using a gradual change to

normal operation instead of the abrupt change [14][15][22].

The switching control can be completed by the modied wind

farm level control too. However, the set points of switching

time, inertial power of inertial controllers and speed

adjustment rates of droop controllers ae considered to be the

local control signals instead. The distribution strategy of the

modied wind farm level control is much more complex than

the equitable distribution ad is determined by the current

rotational speed, the number of selected wind turbines and the

system requirement, etc.

Deloading of wind turbines means increased wear and tearof the blade and hub material due to the equent pitch control

[38] as well as a generation loss because not all available wind

energy is converted into electricity. The use of ESS reducesthe generation loss but leads to a higher investment and

maintenance cost. In addition, no energy storage is 100%

ecient which also cause some losses [31]. Therefore, the

economic benets need to be optimized considering the above

factors.

Actually, not all the wind turbines in the wind farm are

necessa to operate at deloading. The number of selected

wind turbines and their deloading extent, i.e., the ratio

between PWTttal and PESStta! in (8), are determined by the

system operation, wind speed, ESS capabili and economybenets.

The equency control support by ESS is limited due to the

little capacity of ESS. ESSs may reduce the equencyexcursion for a while but cannot permanently inuence the

steady state equency. Therefore, conventional power and

wind power should be rectied to support the long-termequency control [31].

The wind farm level control can send the appropriate

commands to the local generating units from a global vision.

In this strategy, the wind turbines can operate in the best

condition for the equency control which cannot be obtained

om the point of view of wind turbine level control.

IV. P SY L CN

So far, most of the studies are related to the wind turbine

and wind farm level controls and few studies focus on thesystem level equency control considering the wind power

penetration. Almost all of the relevant research on system

level control observed the impact of increasing wind power on

equency stability [2][8][39] or proposed the simple

coordination control method between the wind farm and

conventional plants [7][40].

In this paper, the equency control is deemed to be

composed of primary and secondary control during thedynamic and quasi-steady state processes within 30 minutes.


6/8

Therefore, the economic dispatch, i.e., the so-called tertiary

control, is not taken into account.

A Wind-Thermal Coordination Control

The secondary control is concerned for the power system

level control to restore the equency to 50 Hz, so the loadreference should be regulated. The inertial control increases

the system inertia but the inertial power may mask the load

changes for a few seconds because of the considerably

released kinetic energy om the rotating mass. Therefore, the

synchronous generators may delay their responses to the

equency events [7].

A enhanced solution as shown in Fig. 11 [7][20][40] is tolet the AGC-controlled thermal plats be aware of the

equency control support by the wind farm as soon as

possible. The wind farm is equivalent to an individual wind

turbine with droop and inertial controllers. The two additional

controllers may be enough to improve the equency stabili.

However, the wind-thermal coordination control can achievean even better equency behavior. The droop control changes

the power reference of the wind farm as well as communicates

Wsys Ineial ontrol

6

with a selected set of AGC-controlled thermal plants through

the coordination control. The droop power P is distributed

by the coordination control as follows:"K =1L.el

(12)

(13)where Pci is the coordination control signal, Kci is theparticipation factor for each thermal plant supporting the wind

farm. Pcimodies the AGC error which is similar to the areacontrol error (ACE).

In this way, the thermal plants will realize the power

imbalance since the very beginning. Therefore, the thermal

plants will start earlier to support the equency control and

the equency can be controlled and recovered back to 50 Hz

faster than for the no coordination control condition.

The wind-thermal coordination control is based on the same

principle as the tie line bias control. However, the AGC error

uses the coordination control signal Pci instead of the tie linepower deviation.

Pc1

AGC.-6fPc; _J+)_- r----Ispd I govo IPeN Lod c

'--Wd frm

(quvt o sg wd ub)Coodato coto AGC-cood

ha pt

Fig. 11. Coordination control btwn wind f and thrmal plants.

B. Wind Power Penetration Impact on Frequency Stabili

During a equency drop, the inertial response of xed

speed wind turbines is much smaller and slower than the

inertial response of synchronous generators because the

allowable slip of 1%-2% for the wind turbine reduces the

coupling of the rotational speed and system equency. The

variable speed wind turbines without wind turbine levelcontrol show negligible inertial response due to the

decoupling between rotational speed and the system equency.

Therefore, the maximum equency change rate is sensitive to

the amount of installed wind power. The power system with

more wind power penetration leads to the greater equency

change rate which has little to do with the ratio between

variable speed and xed speed wind turbines. The equency

nadir for the system with only xed speed wind turbines

reaches the same level as for the no wind power condition.

However, the equency nadir is considerably lower if more

variable speed wind turbines are integrated into the grid. Thus,

the maximum equency change rate and equency nadir

events may increase in the future as the wind power

penetration increases. The additional controllers on the

variable speed wind turbines can effectively reduce the

equency change rate and nadir. The benecial eect of the

large amount of kinetic energy stored in wind turbines could

be of signicant importance if the energy were utilized in a

large-scale way [2][8][39].

ONCLUSONSThis paper presents a review on the equency control of

power system with wind power penetration. The control

strategies in the recent studies can be separated into wind

turbine, wind farm and power system levels.

The wind turbine level control supports the prima

equency control. The inertial, droop and deloading

controllers are installed on the power electronic converters of

variable speed wind turbines or pitch controllers of all kinds

of wind turbines. The inertial control emulates the "hidden

inertia or fast power reserve to slow down the equency

change rate in the transient process. The equency nadir can

be increased by both inertial control and droop control. Thedeloading possibilities are achieved by two approaches of


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overspeeding and pitching. The deloading control stores the

deloaded power as reserves for the wind farm to reduce the

steady state equency deviation. The restrictions of the wind

turbine level controllers are also discussed.

The wind farm level control is composed of central control

and local control. The central controller receives the activepower command om operators or AGe and distributes the

command to the local controllers. The local control refers to

the wind turbine deloading control and ESS control. The local

control ensures the distribution signal for the desired

generation of wind turbines and ESSs in the wind farm. The

modied wind farm level control is also presented to

overcome the restrictions of the droop control and inertial

control. The factors which affect the distribution strategy are

rther reviewed om the point of view of economy and

technology.

The power system level control supports the seconda

equency control. Only the wind-thermal coordination controlmethod is presented due to the little research in relation to the

area of system level control. The inertial power which is

released by the inertial control may transiently mask the load

changes and the thermal plants may delay their response to the

equency events. However, the thermal plants can be started

earlier to support the wind farm by the coordination control

and the frequency can be recovered to 50 Hz faster than for

the no coordination case. The coordination control is based on

the same principle as the tie line bias control. The wind

penetration impact on the equency stability is also described.

Therefore, the equency securi indices of change rate,

nadir and steady state deviation are maintained at the

appropriate values by using the 3-level control methods.

VI. ACNOLEDENTS

This work was supported by Vestas Technology R&DSingapore Pte Ltd.

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VIII.ORPHES

Yuan-zhang SUN (M99SM01) rcivd th B.S. dgr frm WuhanUnivrsity of Hydro and Elctrical Enginring, China, th M. S. dgr frmElctric Powr Rsarch nstitut (EPR), China, ad Ph.D. dgr om

Tsinghua Univrsity, Bijing, in 1978, 1982, and 1988, rspctivly, all inlctrical nginring. H is now a chair profssor at Tsinghua Univrsity anddan of School of Elctrical Enginring at Wuhan Univrsity. His mainrsarch intrsts ar in th aras of powr systms dynamics ad contrl,voltag stability and control, ad rnwabl nrgy.

Zhao-sui NG rcivd th B.S. dgr in lctrical nginring omTsinghua Univrsity, Bijing, P. R. China in 2009. H is now a Ph. D.candidat at Tsinghua Univrsity. His main rsarch intrsts ar rnwablnrgy and th stability analysis on powr systms.

Guo-jie LI rcivd his B.S. and M.S. dgrs in Elctrical Enginring fromTsinghua Univrsity, P.R. China in 1989 and 1993, rspctivly. H alsorcivd Ph. D. dgr in th School of Elctrical and Elctrnic Enginring,Nanyang Tchnological Univrsity Singapor in 1999. H is now an associat

prfssor in th Dparmnt of Elctrical Enginring, Tsinghua Univrsity, P.R. China. His currnt rsarch intrsts includ powr systm analysis andcontrol, wind powr analysis d control, and powr quality.

Jin LIN rcivd th B.S. dgr in lctrical nginring om TsinghuaUnivrsity, Bijing, P.R. China in 2007. H is now a Ph. D. candidat atTsinghua Univrsity. His main rsarch intrsts ar rnwabl nrgy and thstability analysis on powr systms.

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review on frequency control of power systems with wind power penetration51

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