Dynamic stability improvement of a multi machine power system connected with a large scale offshore wind farm using a generalized inified power flow controller (tt)

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National Cheng Kung University Department of Electrical Engineering

Tainan City, Tarwan, R O C

Master of Science Thesis

Dynamic-Stability Improvement of a Multi-machine Power System connected with a Large-scale Offshore Wind Farm

Using a Generalized Unified Power Flow

Controller

Student: Nguyen Thị Ha Advisor: Li Wang

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Dynamic-Stability Improvement of a Multi-machine Power System connected with a Large-scale Offshore Wind Farm Using a Generalized Unified Power Flow

Controller

Nguyen Thi Ha* and Li Wang**

Department of Electrical Engineering National Cheng Kung University

Tainan City, Taiwan, R O C

Abstract

This thesis studies the dynamic-stability improvement of a multi-machine system connected with a large-scale offshore wind farm based on doubly-fed induction generator (DFIG) using a generalized unified power-flow controller (GUPFC) A two- area four-generator system model is employed as the studied multi-machine system Two proportional-integral-derivative (PID) damping controllers and two fuzzy logic controllers (FLCs) of the proposed GUPFC are respectively designed to improve the stability of the studied multi-machine power system connected with the offshore wind farm under different operating conditions

A frequency-domain approach based on a linearized system model using eigenvalue analysis and a time-domain method based on nonlinear-model simulations subject to various disturbances are both performed to examine the effectiveness of the proposed GUPFC combined with the designed damping controllers

It can be concluded from the comparative simulation results that the proposed GUPFC joined with the designed FLCs demonstrates better damping performance for improving the stability of the studied multi-machine system subject to different disturbances than the designed PID damping controllers

Keywords: Multi-machine system, wind farm, doubly-fed induction generator, generalized unified power-flow controller, dynamic stability, flexible AC transmission systems

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ACKNOWLEDGEMENTS

First of all, I would like to express my deep gratitude to my advisor Professor Li Wang for his help, his advice and his teaching His valuable suggestions, his encouragement and his patience have been a big help for me over the last time

I am very grateful to all Professors in Power Group of Electrical Engineering Department, National Cheng Kung University (NCKU) as well as Professors from other Universities for their teaching, encouragement, and valuable comments

I also would like to thank my colleagues at the laboratory for the enjoyable discussions and friendly atmosphere

Furthermore, I would like to extend my deepest gratitude and personal thanks to those closest to me In particular, | would like to thank my families for their support, encouragement and understanding

Last but not least, I would like to say special thanks to the NCKU Scholarship Program for giving me the opportunity to work on a highly studying environment and for their financial support

Nguyen Thi Ha

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2.3.4 Mass-Spring-Damper Model 00.cccccccccccssseccecensseeeeeeesssseeeeeenssaeees 18 2.3.5 Doubly-fed Iinduction øenerafor model .- - - - «<< s++++<<ssssssa 18 2.3.6 Back-to-back converfter model .- - - - cc 1c 11122 1111111111111 rre 20

“EWĐ ©9000 1 4 21

"Ti can 0 vi 22

2.3.9 Pitch angle contrỌÏ€T - - + - 22 1113222211113 2321111113553 11111551 krrrg 24 2.4 GUPFC mođel c0 2211121211 112211 1121111111 11111 11111111111 K KH KH KH KH khe 25 2.4.1 Mathematical model of a GUPFC 2c 2211122211115 25 2.4.2 GUPFC power flow contfrolÏer - + + c s3 s3 ksssesexeecea 28

“No (0y gì): 1 30

Chapter 3 Design of oscillation damping controllers for GUPFC 33 3.1 Design oftwo PID controllers for GUPFEFC c5 55552225 **£+++zseeeceszeessss 33 3.2 Analysis of closed-loop system eIgenvalue senSIfIVIfles - 40 3.3 Design oftwo FLC controllers for GUPEC 55 52225 ***+++sseeccszeeesse 45 Chapter 4 Steady-state analysis of the system under various

O0perafing COI(ÏÍ{ÏOIIS s- << 5 S 6 99999096 96 6 0 09689899949696608886886999990966 49 4.1 Power flow calculation under the steady-state condition of the system 49 4.2 Different operating actrve power conditlons of SGs -<«- 50 4.3 Various terminal voltàes Of SS - 2c 1112222221111 12 S211 vn vn gưưky 69 4.4 Different wInd-speed cond1fIO'S - - - c2 2 2222223111113 kkkeeerska 85 4.5 Various operating terminal voltages of DFÏG .- - << << + +++5<<scc<sss2 98 Chapter 5Š Tìme-domain SIITuÏ2ÏOIIS s55 << << 5 5 S66 6599996 €63999699595958866669469966 104 5.1 Disturbance on input mechanical torques of SG s - +55 ++<<<<<s5: 104 5.2 Three-phase short-circuit fault at transmission line without changing

90/0 0305/1000 oo ốỐốố.ốỐốỐốỐ.ố.ố.Ềẻ aAAA 113 5.3 Three-phase short-circuit fault at transmission line with changing network

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LIST OF FIGURES Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20

Configuration of the sySfeim - - - c2 2 2223111113353 111115825111 re 8

Single-line diagram of the studied two-area four-generator system 9

Block diagram of the two-axIs model of the SG . - «- 10

Block diagram of the IEEE type I excitation sysfem - 11

SIngle-reheat tandem-compound steam turbine model 13

Speed-governor model for steam turbine . - =<++++ 5+ 14 One-line diagram of wind DFIG driven by a VSWT through a GB 15

Simplified reduced-order two-mass model of WT drive train 18

DFIG a-ax1s equ1valennf GITCUIĂ . - 55 2-22 * 3+ S++2<++seeeeeeeeeea 19 Model of back-to-back co'nV€Tf€T - -.- 2c 1 2221132211132 xrerke 20 Control block diagram of the RSC controller - +55 -+<<<<s5: 22 Stator-flux-oriented reference Írame . - - + c1 S2 ssssree 22 Contfrol block diagram of the GSC controller - 5-55 5552 +<<<sss2 23 Stator-voltage-oriented reference Írame - - << + + s2 +22 ssss+ 24 Control block diagram of pitch angle controlÏer - <<ss- 24 Operation principle of the GUPEC with three converters 26 The equivalent circuit of the GŒUPEC 55 5-2251 2 322222 c+szseseees 26 Control block diagram Of GŒUPFFC - + - 21133 *++22EE++seeeeeeseeeexse 29 Integration of models into the sysfem + 52225 + + ++++scccszse2 3l Transformation from the i-th generator’s rotor reference frame to

the common D-Q reference Írame .- - + + 222222221 eeesszees 32

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Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig 3.1 3.2 3.3 3.4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

The control block diagram of the phase angle a@,, of the GUPFC

including PID controlÏersS - - 2c 223223133222 vkeeexeeessss 34 Fuzzy loglc controller s†ruCfUTe - 52+ + + + s++2*++seeeeeeersea 45 The control block diagram of the phase angle ø„ of the GUPFC

Iincluding F LLCS - - - + 2211111222311 1111 1251111115901 1111101 111kg vn 47 Membership functions for the two proposed FLCs 48 The configuration of system w1thout GUPFEC 27 < <5 5 52+<<<sssss+ 52 The configuration of system with GUPEFC - 755555222 s+c<ssexs2 52 Power flow of the system under different active powers

Power flow of the system without and with GUPFC

under different terminal voltages of S2 -5-+2<<<<<+++<<sssss2 74 Power flow of the system without and with GUPFC

under different terminal voltages of SG 552225 <<<<<++<<<<sss2 79 Power flow of the system without and with GUPFC

under different terminal voltages of SG4 552225 <<<ss++<>sssss2 84 Root locus of oscillatory modes under different wind speed

COTIIẨIOTNS - 2 0 2220111221111211 1121111111111 111 11111111111 1E k 1H kh 96 Power flow of the system without and with GUPFC

under different terminal voltages of DF]G . - 55-25 << <s+<<+s<s2 103 Sequence of the applied torque disturbances of SGs - 106 Dynamic responses of the system subject to torque

disturbances on SGs’ input mechanical torques without

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Fig Fig Fig Fig Fig Fig Fig 5.3 5.4 5.5 5.6 5.7 5.8 5.9

and with GUPEC . 2 1 2201112211 112511 121111211 11111 11111111111 1911 EHrvkt 106 Dynamic responses of the system subject to torque

disturbances on SGs’ input mechanical torques with

GUPFC and with GUPFCTPIIS 20 2221112211 112111111 E111 ekred 109 Dynamic responses of the system subject to torque

disturbances on SGs’ input mechanical torques with

GUPFC+PIDs and with GUPFC+H+FLCS 00 ecccecccececeeeeeeeeneeenteeeeeees 111 Transient responses of the system subject to a

three-phase short-circuit fault at one of parallel transmission line 10-11 without changing network

structure without and with GUPPEFC c2 2 222 2222 E2 EE*svrssreeed 114 Transient responses of the system subject to a

three-phase short-circuit fault at one of parallel transmission line 10-11 without changing network

structure with GUPFC and with GUPFC~+PIIs eect etees 117 Transient responses of the system subject to a

three-phase short-circuit fault at one of parallel transmission line 10-11 without changing

network structure with GUPFC+PIDs and with GUPFC+FLCs 119 Transient responses of the system subject to a

three-phase short-circuit fault at one of parallel transmission line 10-11 with changing network

structure without and with GUPEFC c2 2221112211251 EEsxkred 122 Transient responses of the system subject to a

three-phase short-circuit fault at one of parallel transmission line 10-11 with changing network

structure with GUPFC and with GUPFC+PIDS 000 cc ceeeeeeeee eee 125

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Fig 5.10 Fig 5.11 Fig 5.12 Fig 5.13 Fig 5.14

Transient responses of the system subject to a three-phase short-circuit fault at one of parallel transmission line 10-11 with changing

network structure with GUPFC+PIDs and with GUPFC+FLCs 127 Wind-speed Var1afIO'S - - - 2c 2 2211122232231 11 3553111111158 1 1kg 129 Dynamic responses of the system under the variations

of wind speed without and with ŒUPFC - 5 25c <2 + + 2+<sseecessssa 130 Dynamic responses of the system under the variations

of wind speed with GUPFC and with GUPFC+PIDs - 132 Dynamic responses of the system under the variations

Of wind speed with GUPFC+PIDs and with GUPFC+FLCs 134

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LIST OF TABLES Table 3.1 Table 3.2 Table 3.3 Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 4.9 Table 4.10

Eigenvalues (rad/s) of the system without GUPFC, with

GUPEC, and with GUPFC and the designed PIIs 5-55 5+ 37 RSCs of the closed-loop system eigenvalues with respect

to the two designed PII”s paramef€rs - - ¿5 c1 3222 sex Al Control rules of the studied FLCS - 2 2c 3+2 +2 +sersreresrses 48 Power flow calculation of the system w1ithout GUPFC - 51 Power flow calculation of the system with GUPEC 55 -2-<<- 51 Steady-state operating points of the system without

and with GUPFC under different active powers of SG2 54 Steady-state operating points of the system without

and with GUPFC under different active powers of SG3 59 Steady-state operating points of the system without

and with GUPFC under different active powers of SG4 64 Steady-state operating points of the system without

and with GUPFC under different terminal voltages of SG2 70 Steady-state operating points of the system without

and with GUPEC under different terminal voltages of SG3 75 Steady-state operating points of the system without

and with GUPEC under different terminal voltages of SG4 80 Eigenvalues (rad/s) of the studied system without GUPFC

under different wind speeds - - c5 211132132231 + cserekg 87 Eigenvalues (rad/s) of the system with GUPFC

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Table 4.11 Steady-state operating points of the system without and

with GUPFC under different operating voltages of DF]G 99

Table A.I Employed system parameters for four-machine sysfem 143

Table A.2 Employed system parameters for transmission Ïine 144

Table A3 Employed system parameters for DFIG-based OWE 144 Table A.4 Employed constanfs for power coefficienfts of WTT 2.« 145 Table A.5 Employed system parameters for ŒUPFC 555222 <<sss++<+>sss2 145

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NOMENCLATURE CV DFI DFIG DML EMTP FACTS FLC GUPFC GB GSC HP IGBT IP IPFC IV KB LP ODC OMIB OWF PID PMSG PWM RMS Control valve Defuzzier interface Doubly-fed induction generator Decision-making logic

Electromagnetic transients program Flexible AC transmission systems Fuzzy logic controller

Generalized unified power flow controller Gearbox Grid-side converter High-pressure turbine Insulated gate bipolar transistor Intermediate-pressure turbine Interline power-flow controller Intercept valve Knowledge base Low-pressure turbine Oscillation damping controller One-machine infinite-bus Offshore wind farm

Proportional integral derivative

Permanent-magnet synchronous generators

Pulse-width modulation Root mean square

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RSC SG SSSC UPFC VSC VSWT TQD WT WECS Rotor-side converter Synchronous generator

Static synchronous series compensator Unified power flow controller

Voltage source converter

Variable-speed wind turbine Torque disturbance

Wind turbine

Wind energy conversion system

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LIST OF SYMBOLS = Đ gr XN — 3U Mechanical torque of SG Electromagnetic torque of SG Field winding voltage of SG

Exciter output voltage

Rotor angle of SG (deg.) Eigenvalues (rad/s) Intermediate variables used in subsystems model of SG Wind speed Power coefficient of WT Tip speed ratio of WT Pitch angle of WT Mechanical power of WT Mechanical torque of WT

Stator (terminal) voltage of DFIG Stator current of DFIG

Stator active power of DFIG Stator reactive power of DFIG

Rotor voltage of DFIG Rotor current of DFIG

Rotor active power of DFIG

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Vực

Kp, K; Ky

Rotor reactive power of DFIG Grid-side converter voltage of DFIG

Grid-side converter current of DFIG

Grid-side converter active power of DFIG

Grid-side converter reactive power of DFIG

Total active power of DFIG Total reactive power of DFIG

Electromagnetic torque of DFIG

Rotational speed of WT Shaft twist angle of WT-DFIG Rotor speed of DFIG

Rotor slip of DFIG

DC-link voltage between RSC and GSC of DFIG

Intermediate variables used in controller model of DFIG

Series injected voltage by GUPFC Shunt injected voltage by GUPFC

Phase angle of series injected voltage by GUPFC

Phase angle of shunt injected voltage by GUPFC DC-capacitor voltage of GUPFC

Base angular frequency

Synchronous speed (@, = 1.0pu)

Gains of PID damping controller

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Ly Washout-term time constant of PID damping controller (s) Đ The number of pole pairs

The dot notation is used to signify derivatives with respect to time ¢, for example, dx

x= — at