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    1186 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 26, NO. 3, AUGUST 2011

    A Nonlinear Voltage Regulator With One TunableParameter for Multimachine Power Systems

    Gurunath Gurrala, Graduate Student Member, IEEE, and Indraneel Sen

    AbstractThis paper proposes a nonlinear voltage regulatorwith one tunable parameter for multimachine power systems.Based on output feedback linearization, this regulator can achievesimultaneous voltage regulation and small-signal performanceobjectives. Conventionally output feedback linearization has beenused for voltage regulator design by taking infinite bus voltageas reference. Unfortunately, this controller has poor small-signalperformance and cannot be applied to multimachine systemswithout the estimation of the equivalent external reactance seenfrom the generator. This paper proposes a voltage regulatordesign by redefining the rotor angle at each generator with respectto the secondary voltage of the step-up transformer as referenceinstead of a common synchronously rotating reference frame.

    Using synchronizing and damping torques analysis, we show thatthe proposed voltage regulator achieves simultaneous voltageregulation and damping performance over a range of system andoperating conditions by controlling the relative angle between thegenerator internal voltage angle and the secondary voltage ofthe step up transformer. The performance of the proposed voltageregulator is evaluated on a single machine infinite bus system andtwo widely used multimachine test systems.

    Index TermsFeedback linearization, power system stabilizers,small-signal stability, transient stability.

    NOMENCLATURE

    Rotor angle (in electrical radians).

    Rotor (electrical) speed, corresponding to

    the time derivative of .

    Rotor angle with respect to the secondary

    voltage of the transformer.

    Slip speed .

    w.r.t. center of inertia (COI)

    .

    w.r.t. center of inertia

    .

    Mechanical and electrical torques.

    Damping coefficient.

    Transient induced voltages due to field

    flux-linkages.

    Manuscript received December 25, 2009; revised January 01, 2010, January05, 2010, April 09, 2010, and July 02, 2010; accepted July 20, 2010. Date ofpublication October 14, 2010; date of current version July 22, 2011. Paper no.TPWRS-01007-2009.

    The authors are with the Department of Electrical Engineering, Indian In-stitute of Science, Bangalore 560012, India (e-mail: [email protected];[email protected]).

    Digital Object Identifier 10.1109/TPWRS.2010.2069930

    d, q-axis components of stator current.

    d, q-axis open circuit time constants.

    d, q-axis reactances.

    Field voltage.

    Voltage measured at the generator terminal.

    Voltage measured at the secondary of the

    transformer.

    Reference voltage.

    PSS input.

    Armature resistance.

    Transformer and transmission line

    reactances.

    d, q-axis components of terminal voltage.

    Gain and time constants of static excitation

    system.

    Inertia constant of machine.

    Power factor at the transformer bus.

    Real and reactive powers at machine andtransformer secondary terminals.

    PSS Power system stabilizer.

    AVR Automatic voltage regulator.

    FBL Feedback linearization.

    SMIB Single machine infinite bus system.

    GEN, SYS Generator, system.

    I. INTRODUCTION

    TRADITIONALLY, the automatic voltage regulator (AVR)and power system stabilizer (PSS) have been designed

    separately using the linearized models of power system. The

    AVR tries to modulate reactive power and PSS tries to modu-

    late real power, since both strategies are executed through field

    voltage, simultaneous achievement of both goals is not pos-

    sible [1], [2]. The linearized models on which the controllers are

    based depend upon the system operating condition. Any signif-

    icant deviation from this nominal operating condition can con-

    siderably degrade the performance of the controllers.

    In order to overcome these difficulties, feedback lineariza-

    tion (FBL) technique has been widely used for generator ex-

    citation system design [3][9]. Most of the nonlinear control

    0885-8950/$26.00 2010 IEEE

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    GURRALA AND SEN: NONLINEAR VOLTAGE REGULATOR WITH ONE TUNABLE PARAMETER 1187

    designs based on FBL have formulated the excitation control

    problem as a regulator problem and terminal voltage regulation

    was not considered in the design objective. As this formulation

    results in poor voltage regulation [2], [8], [10], [11], researchers

    have proposed several alternative methods for voltage regula-

    tion in addition to FBL, such as using observed decoupled state

    space, switching an additional controller after the fault, etc. [2],[5][8], [11][14]. Most of these controllers require complete

    system information for the design, and at least two variables

    need to be tuned for better performance. It is always desirable

    to have a single controller with minimum tunable parameters

    that can simultaneously achieve better terminal voltage regula-

    tion and good small signal performance. The first attempt in this

    direction was made in [10]. Unfortunately, this controller has

    poor small-signal performance and cannot be applied to multi-

    machine systems without the estimation of equivalent external

    reactance seen from the generator terminals.

    In [15], a power system stabilizer based on feedback lin-

    earization has been proposed by taking secondary voltage of

    the step up transformer as reference instead of the infinite busvoltage. This PSS tries to control the oscillations by controlling

    the angle , the angle between generator internal

    voltage , and secondary voltage of the step up transformer

    . This work has been patented [16] with hardware imple-

    mentation details. In [17], this concept has been used for de-

    veloping fixed parameter power system stabilizers for multima-

    chine systems.

    In this paper, a nonlinear voltage regulator design for mul-

    timachine systems has been proposed by taking the secondary

    voltage of the step-up transformer (high-voltage bus) as refer-

    ence [16], [17] instead of a common synchronously rotating ref-

    erence frame [infinite bus voltage in the case of single machineinfinite bus system (SMIB)]. Using the concepts of synchro-

    nizing and damping torques, it has been shown that the tuning

    parameter of the proposed controller can be varied in a wide

    range as opposed to the controller in [10] which allows effective

    tradeoff between the voltage regulation and small-signal per-

    formance objectives. The performance of the proposed voltage

    regulator has been evaluated on an SMIB test system and two

    most widely used multimachine test systems, IEEE ten-gener-

    ator 39-bus system and IEEE 16-generator 59-bus system over

    a wide range of operating conditions.

    II. PROPOSED APPROACH

    In this paper, a generator connected to an external power

    system through a step-up transformer as shown in Fig. 1 has

    been considered for the nonlinear AVR design [15], [17]. In the

    present design, IEEE Model 1.0 [18], [19] is used to represent

    the synchronous generator. This results in a third-order dynamic

    model for a power system. The use of third-order model is jus-

    tified as it sufficiently represents the essential dynamics of the

    system. In systems equipped with static excitation systems, the

    complexity of higher order models is largely due to the pres-

    ence of amortisseur windings which always contribute to posi-

    tive damping. The adequacy of third-order model has been ex-

    perimentally verified recently in [20] and a large number of non-

    linear excitation controllers are designed based on this model

    [17], [21].The generator rotor angle with respect to the secondary

    voltage of the transformer is defined as .

    The expressions for are given below [17]. Subscript

    refers to the th machine in a multimachine environment:

    (1)

    where and is

    power factor angle at the high-voltage bus:

    (2)

    The expressions for and are as follows:

    (3)

    where

    Now the expression for terminal voltage is given by (4) at the

    bottom of the page.

    The variables have standard meaning as indicated in the

    nomenclature. We use input-output feedback linearization to

    derive the nonlinear control law for the field voltage. For a

    control affine system with output ,

    the basic approach of the input-output feedback linearization is

    to differentiate the output function repeatedly until the input

    appears and then design to cancel the nonlinearity. The

    number of differentiations required for the input to appear is

    called the relative degree of the system. Defining the tracking

    (4)

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    1188 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 26, NO. 3, AUGUST 2011

    Fig. 1. Generator connected to external network through a step-up transformerand proposed control structure.

    error as , where is the desired output, a

    fixed gain parameter can be chosen such that the error

    dynamics as . Solving the error dynamics

    equation gives the nonlinear control law as

    (5)

    Derivatives of the output (4) are taken successively until the

    control input appears in the equation. In this case, relative

    degree is one. Taking derivative of (4), we get

    (6)

    Equation (6) can be written in control affine form as

    (7)

    Here the output to be tracked is the steady-state terminal voltage

    (the reference voltage). So the tracking error is defined as

    . Following assumptions are made in the design.

    1) is replaced with . This

    is to enable a damping torque component to be produced

    on the rotor.

    2) . This assumption is to avoid singularity in the

    nonlinear control law during sudden changes in terminalvoltage.

    Solving the error dynamics equation, one can get the nonlinear

    control law from (5) for field voltage as given in the fol-

    lowing:

    (8)

    The subscript 0 indicates initial operating condition. The pro-

    posed control structure has been shown in Fig. 1. The control

    law tries to control instead of . The proposed controller can

    assess the system disturbances such as changes in system con-

    figuration or load variations based on the deviations in com-

    puted from the power flow and voltage at the high-voltage bus

    of the step-up transformer [15], [17]. In general, it is very diffi-

    cult to get the measurements of and in the field. However,

    the proposed approach enables us to realize the control law inmultimachine environment by computing (1)(3) from

    and measurements at the high-voltage bus of each machine.

    This makes the control law decentralized. Usage of (1) and (2)

    for power system control applications has been patented [16].

    The conventional nonlinear AVR proposed in [10] and the

    proposed AVR have the same control format except that the

    former is a function of and the later is a function of

    . The proposed controller has shown much better performance

    than the conventional nonlinear AVR and the linear

    controller. In the following section, the concepts of synchro-

    nizing and damping torques have been used to understand the

    reason for better performance of the proposed controller.

    III. ANALYSIS OF THE PROPOSED NONLINEAR AVR

    To understand the small-signal behavior of the proposed non-

    linear AVR at different operating conditions, the control law (8)

    is linearized using the conventional Taylor series approxima-

    tion. The analysis is performed for SMIB system (subscript i

    is dropped). Linearization of (8) gives

    (9)

    In implementing the nonlinear control law (8), terminal

    voltage is obtained from the measurements at the generator

    terminals, so the linearized equation of is

    (10)

    (11)

    (12)

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    GURRALA AND SEN: NONLINEAR VOLTAGE REGULATOR WITH ONE TUNABLE PARAMETER 1189

    While linearizing , it is considered as a function of

    and . While linearizing , we consider and as state vari-

    ables and as a variable quantity. So linearizing given in

    (3) results in

    (13)

    It can be observed that an additional term also comes in the

    expression to account for the variations in and the respective

    constants are functions of and :

    (14)

    substituting (10) and (13) in (9) and rearranging the terms, one

    can arrive at (15) where and

    . This equation can be rewritten as (15)and (16) at the bottom of the page.

    Fig. 2 shows the block diagram representation of (16). From

    the block diagram, the proposed controller can be interpreted

    as a high gain , fast exciter with negligible delay. It has

    four components negatively affecting the torque angle loop, two

    components due to the deviations in rotor angle and relative

    rotor angle denoted by and , respectively. One com-

    ponent due to the deviations in flux linkages denoted by

    and one component denoted by due to the deviations in

    voltage magnitude of the high-voltage bus . and are

    standard Heffron Phillips model parameters [23]. It also con-

    tains an additional component from the deviations in slip

    speed as shown with dashed circle in Fig. 2. This compo-

    nent contributes positively to the torque angle loop just like

    a power system stabilizer. In case of a conventional FBLAVR

    ,the components and are contributed by and the com-

    ponent is zero as is constant.

    For simplifying the analysis, though and have dif-

    ferent magnitudes, one can combine the effect of these com-

    ponents by taking . This does not affect the

    Fig. 2. Proposed feedback linearization based AVR.

    synchronizing and damping torques analysis as and arein-phase quantities.

    Variations of parameters and are plotted by

    varying generator power from 0.5 p.u. to 1.1 p.u. for various

    values of . The terminal voltage is fixed at 1 p.u. Figs. 3

    and 4 show the variations of and , respectively,

    with . Gain of the proposed controller is fixed at 20 so

    that the variation of and is almost the same as that of the

    linear AVR parameters and . Observe that and are

    always positive. and onthe other handcan bepositive or

    negative (see Fig. 3). Here the negative damping contribution of

    has to be compensated by the component for damping.

    These plots for conventional FBLAVR are not shown due to

    space limitations; however, they are observed to be more or less

    identical to that of the proposed FBLAVR.

    Fig. 5 shows the variation of with for different values

    of . Solid lines show the variations for the proposed non-

    linear AVR. Dashed lines show the variation for the conven-

    tional nonlinear AVR. It can be seen that the damping com-

    ponent of conventional FBLAVR reduces significantly with in-

    crease in external impedance and with increase in system

    (15)

    (16)

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    1190 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 26, NO. 3, AUGUST 2011

    Fig. 3. Variation of with for various values of .

    Fig. 4. Variation of with for various values of .

    loading. However, the damping term contribution of the pro-posed AVR is more or less constant with increase in loading

    as well as system external reactance. The proposed controller,

    therefore, offers good damping performance over a wide range

    of operating and system conditions. It has been observed that for

    in the range of 0.2 p.u. to 0.8 p.u., lies between 620

    and 950. Higher values of gain give higher synchronizing torque

    and better voltage regulation but at the expense of damping

    torque [23]. It has been observed that , which represents the

    effect of variation in the magnitude of the voltage of the trans-

    former bus, varies between 5e-4 to 13e-4. It means that the vari-

    ation in voltage magnitude of the high-voltage bus on system

    dynamic performance is not of much significance. Neglecting

    variation while deriving the proposed control law (assump-tion 2) is thus justified.

    Fig. 5. Variation of with of proposed FBLAVR and conventionalFBLAVR.

    A. Synchronizing and Damping Torques AnalysisThe component of electrical torque produced by voltage reg-

    ulator action due to variations in rotor angle through can be

    expressed as [26]

    (17)

    The first component can be treated as the torque that

    would have been produced by a static AVR with a gain equal

    to and low time constant. The second component

    can be considered as the torque produced by due to the non-

    linear AVR action. Substituting (complex eigen-

    value corresponding to the rotor mode of system matrix that

    can be easily obtained) and , one can ob-

    tain the following expressions for synchronizing and damping

    torque coefficients [26]:

    (18)

    (19)

    Total synchronizing torque coefficient can be obtained by

    adding to (18).

    Figs. 6 and 7 show the variation of total synchronizing anddamping torque coefficients and with for various

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    GURRALA AND SEN: NONLINEAR VOLTAGE REGULATOR WITH ONE TUNABLE PARAMETER 1191

    Fig. 6. of proposed FBLAVR and conventional FBLAVR.

    Fig. 7. of proposed FBLAVR and conventional FBLAVR.

    values of . It can be observed that the variation of the

    proposed AVR is the same as that of a conventional nonlinear

    AVR except for . decreases with increase in

    for both controllers; however, for the proposed AVR, the is

    always positive and much higher than that of the conventional

    FBLAVR. Positive over the entire range of operating condi-

    tions accounts for the better performance of the proposed non-

    linear AVR.

    Now we analyze the damping factor obtained from the total

    and using the following expression [26]:

    (20)

    Fig.8 showsthecomparison of withincrease in for the pro-

    posed FBLAVR and the conventional FBLAVR. Observe that

    for both the controllers at every value of , the variation in

    damping factor has an inverted v-shape. The value of at

    which maximum damping occurs decreases with increase in .

    Observe that variation with the proposed AVR is always pos-

    itive. The maximum damping factor occurs at

    for the nominal operating condition (

    p.u., p.u., and p.u.). This is muchhigher than of conventional FBLAVR. In the

    Fig. 8. Variation of damping factor , proposed FBLAVR.

    case of proposed FBLAVR, the tuning parameter can be

    varied in a wider range than the conventional nonlinear AVR

    because even at , the damping factor is 0.17786 for

    p.u., which is quite acceptable for power systems.

    This allows an effective trade-off between voltage regulation

    and damping improvement.

    IV. SIMULATION RESULTS

    A. SMIB System

    The performance of the proposed AVR (8) has been exten-

    sively evaluated on a SMIB system studied in [23]. Data for the

    steam input SMIB given in [23] have been used here. Several

    operating conditions are created to test the performance of the

    proposed voltage regulator by varying from 0.2 p.u. to 0.8p.u. and from 0.5 p.u. to 1 p.u. by keeping and con-

    stant at 1 p.u. Results of only a few representative test cases are

    shown here.

    Figs. 9 and 10 show the terminal voltage and the field voltage

    responses of the nominal SMIB system (

    p.u., p.u., p.u.) for a 0.1 p.u. step change in

    . The system is operated with 1) nonlinear AVR proposed in

    [10] (conventional FBLAVR), , 2) static

    (linear ),and 3) proposed nonlinear AVR (proposed

    FBLAVR or FBLAVR), . The system is unstable with

    linear AVR alone. The system becomes stable with all the three

    controllers. It can be observed that the performance of the pro-posed controller is comparable to the linear and the

    conventional nonlinear AVR. Observe that all the controllers are

    able to track the reference voltage perfectly. In Fig. 10, observe

    that the control effort due to the proposed voltage regulator is

    similar to that of the linear .

    It has been observed in simulations that if assumption 1 is not

    considered, then the performance of the proposed controller is

    exactly the same as the conventional nonlinear AVR. Assump-

    tion 1 is very crucial in this design as this enables the proposed

    AVR to achieve good small signal performance.

    Fig. 11 shows the responses of the SMIB with the same con-

    ditions as above, following a fault cleared after two cycles

    by tripping one of the parallel lines. After the fault is cleared,the system becomes weak with an equivalent external reactance

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    1192 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 26, NO. 3, AUGUST 2011

    Fig. 9. response, 10% step change in .

    Fig. 10. response, 10% step change in .

    Fig. 11. response, fault at transformer bus, cleared by line tripping.

    . The system is more oscillatory with conventional

    nonlinear AVR. The performance of the proposed AVR is better

    than the performance of the linear .

    B. Ten-Generator 39-Bus System

    This is a most widely used test system, for validating controldesigns. The data for the system are taken from [19]. Though

    Fig. 12. of GEN-9 for a 0.02 p.u. step change in at GEN-9, 10 GENSYS.

    the controller is developed for third-order model, here the sim-

    ulations are carried out using IEEE model 1.1 [18] neglecting

    transient saliency. All the static excitation systems of the ten-

    generator (GEN) system except GEN-2, which is an equivalent

    representation of external network, are replaced with the pro-

    posed nonlinear AVR. The performance of the proposed non-

    linear AVR is compared with the performance of the system

    equipped with linear AVR+PSS at varied operating conditions.

    is selected such that

    the terminal voltage response of each generator for a 0.02 p.u.

    step change in is within % of the final value [24]. Sim-

    ulation results of a few test cases are shown in this section.

    Fig. 12 shows terminal voltage responses of GEN-9 with

    the proposed AVR for a 0.02 p.u. step change in inputof GEN-9. The figure also contains the responses obtained

    with a linear AVR and linear AVR+PSS. It can be observed

    that the system is unstable with the linear AVR alone. The

    response with the proposed AVR is comparable to that of the

    linear performance. Observe that the response of

    the proposed voltage regulator is much faster than linear AVR

    and linear AVR+PSS. For this case, 0.1% steady-state error is

    observed in the final value.

    From extensive simulation studies, the lines 2122, 2629,

    and 2829 are found to be critical for system stability, and

    few results corresponding to contingencies on these lines are

    presented. Fig. 13 shows the terminal voltage responses ofGEN-9 for a fault of 80 ms duration on bus 29 followed

    by tripping of 2928. In this case, the system with linear

    is more oscillatory. The voltage dynamics are

    considerably improved with the proposed controller, and the

    steady-state error in the post fault voltage is 0.003 p.u.

    Fig. 14 shows the responses of GEN-7 to GEN-10

    under heavy loading conditions. All the loads are increased

    by 15%, and generation at generators 5 to 10 is increased by

    15%. A fault of 70 ms duration on bus 21 followed by

    tripping of 2122 is created. In this case, the system is more

    oscillatory with linear . It has been observed

    that the voltage dynamics are considerably improved. The

    percentage voltage regulation calculated as the percentage de-viation from prefault voltage to the postfault voltage w.r.t. the

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    GURRALA AND SEN: NONLINEAR VOLTAGE REGULATOR WITH ONE TUNABLE PARAMETER 1193

    Fig. 13. of GEN-9 for a fault of 80 ms at bus 29 cleared by tripping line2928, nominal loading, 10 GEN SYS.

    Fig. 14. ofGEN-7to GEN-10for a fault of70 msat bus 21clearedby tripping line 2122, heavy loading, 10 GEN SYS.

    prefault voltage at all generators except at GEN-2 is given by

    which is less than %. Under

    nominal loading conditions, the terminal voltage regulation

    is always less than %. One can still obtain better voltage

    regulation by increasing the gain with little compromise

    on the damping performance; even then, the performance of the

    proposed AVR would be better than the linear .

    Fig. 15 show the rotor angle responses of GEN-1 to

    GEN-3 w.r.t. center of inertia with the proposed AVR for a

    fault of 100 ms duration on bus 11 followed by tripping of

    11-2 under light loading conditions (all loads are decreased by

    20% and generation at GEN-3 to 10 are decreased by 20%).

    The figure also contains the responses obtained with a linear

    AVR+PSS. It can be observed that the damping performance

    of the proposed controller is similar to the performance of the

    linear .

    C. The 14-Generator 59-Bus System

    This is a simplified model of the southern and eastern Aus-

    tralian network as shown in Fig. 16. It consists of five areas in

    which areas 1 and 2 are closely coupled. The system data aretaken from [25]. The six operating conditions given in [25] are

    Fig. 15. of GEN-1 to GEN-3 for a fault of 100 ms at bus 11 clearedby tripping line 11-2, light loading, 10 GEN SYS.

    Fig. 16. IEEE 14-generator 59-bus test system.

    studied extensively. A few representative results corresponding

    to case 1 (heavy load) and case 4 (light load) are given here. For

    this system, also IEEE model 1.1 [18] is used for synchronous

    generators including transient saliency. The nonlinear AVR gain

    is se-

    lected for simulations.

    Fig. 17 shows the slip speed responses of area-3 gen-

    erators GEN-6 and GEN-7 w.r.t. center of inertia for a 0.1 p.u.

    step change in at GEN-6. This simulation corresponds tocase-1 operating condition. The small-signal performance of the

    proposed nonlinear AVR is better than the linear

    controller which are designed using the complete system infor-

    mation.

    At case-1 operating condition, the line 2931 is a heavily

    loaded line carrying 2760 MW. Fig. 18 shows the responses

    for a fault at bus 31 cleared after 35 ms by tripping one of

    the parallel lines between 31-29. The slip speed responses

    of area-5 generators GEN-13 and GEN-14 w.r.t. the GEN-9 of

    area-4 are shown. The responses are well damped with the pro-

    posed controller within 5 s. The inter area mode ( Hz)

    oscillations of small magnitude persist until 20 s in the case of

    linear . With increase in fault clearing times be-yond 35 ms, both of the controllers eventually fail to stabilize

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    1194 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 26, NO. 3, AUGUST 2011

    Fig. 17. responses of GEN-6 and GEN-7 for a 0.1 p.u. step change inat GEN-6, case-1, 14 GEN SYS.

    Fig. 18. responses of GEN-13 and GEN-14 w.r.t. GEN-9, fault at bus31 cleared after 35 ms by tripping the line 31-29, case-1, 14 GEN SYS.

    the system. This simulation clearly shows the ability of the pro-

    posed nonlinear AVR in damping the interarea mode of oscilla-

    tions. For this condition, a maximum terminal voltage deviation

    of 3.7% has been observed at bus 36.

    Fig. 19showsthe responses for a fault at bus55 for case-4,

    which is a light loading condition. The fault is cleared after 100

    ms by tripping one of the parallel lines between the buses 55

    and 57. Here the responses of GEN-12 to GEN-14 areshown. The responses are well damped in about 3 s with the

    proposed FBLAVR, whereas the oscillations persist until 6 s

    with the linear .

    Extensive simulation studies on multimachine systems have

    clearly established the superiority of the proposed AVR in

    damping interarea modes when compared to the conventional

    nonlinear AVR and linear .

    V. CONCLUSION

    A nonlinear voltage regulator has been proposed in this

    paper for multimachine power systems using output feedback

    linearization approach by redefining the rotor angle at eachgenerator with respect to the secondary voltage of the step-up

    Fig. 19. responses of GEN-12 to GEN-14, fault at bus 55 clearedafter 100 ms by tripping the line 55-57, case-4, 14 GEN SYS.

    transformer as reference instead of a common synchronouslyrotating reference frame. Though the controller is designed

    using third-order model, it has been validated on higher order

    models. The proposed controller has shown better performance

    when compared to the conventional AVR proposed in [10] as

    well as static . From the synchronizing and damping

    torques analysis, it is observed that the proposed AVR always

    produces a positive damping torque and allows considerable

    variation in the tuning parameter so as to get effective trade off

    between the voltage regulation and small signal performance

    objectives. The implementation of this controller is very simple

    as it requires only local measurements. The proposed approach

    for the nonlinear AVR design can replace the conventional

    structure, as tuning a single parameter is alwayseasier than tuning multiple parameters of a power system

    stabilizer in the structure.

    REFERENCES

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    Gurunath Gurrala (GS09) received the B.Tech degree in electrical and elec-tronics engineering from S.V.H. College of Engineering, Nagarjuna University,Guntar, India, in 2001 and the M.Tech degree in electrical power systems fromJ.N.T.U. College of Engineering, Anantapur, India, in 2003.He is currentlypur-suing the Ph.D. at the Indian Institute of Science, Bangalore, India.

    He worked as an Assistant Professor in Anil Neerukonda Institute of Tech-nology and Sciences (ANITS), Visakhapatnam, India, from 2003 to 2005. Hisresearch interests include power system stability, grid integration of renewables,flexible AC transmission systems, artificial intelligence applications to power

    systems, and nonlinear and adaptive control of power systems.

    Indraneel Sen received the Ph.D. degree from IISc, Bangalore, India, in 1981.He is currently an Associate Professor in the Department of Electrical En-

    gineering at the Indian Institute of Science, Bangalore. His research interestsinclude power system stability, adaptive control, and energy management sys-tems.


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