Transient Stability Assessment of Two-Area Power System with LQR based CSC-STATCOM

Transcription

1 Saneep Gupta, Ramesh Kumar Tripathi Transient Stability Assessment of Two-Area Power System with QR base CSC-STATCOM A current source converter (CSC) base static synchronous compensator (STATCOM) is a shunt flexible AC transmission system (FACTS) evice, which has a vital role as a stability support for small an large transient instability in an interconnecte power network. A robust linear quaratic regulator (QR) base controller for CSC- STATCOM is propose. In this paper, QR base CSC-STATCOM is esigne to enhance the transient stability of two-area two-machine power system. First of all, moeling & QR base controller esign for CSC-STATCOM are escribe. After that, the impact of the propose scheme on the test system with ifferent isturbances is emonstrate. The feasibility of the propose scheme is emonstrate through simulation in MATAB an the simulation results show an improvement in the transient stability of power system with CSC-STATCOM. Also, the robustness an effectiveness of CSC-STATCOM are better rather than other shunt FACTS evices (SVC & VSC-STATCOM) in this paper. Key wors: CSC, EAC (equal area criterion), FACTS, QR, STATCOM. Procjena prijelazne stabilnosti voporučnog energetskog sustava s CSC-STATCOM-om zasnovanom na QR-u. Statički sinkroni kompenzator (STATCOM) zasnovan na pretvaraču strujnog izvora (CSC) je urežaj za izmjenični prijenos s fleksibilnim "shuntom" (FACTS), koji značajno oprinosi stabilnosti malih i srenjih prijelaznih nestabilnosti u mežusobno povezanoj energetskoj mreži. Ovje je preložen robusni sustav upravljanja zasnovan na linearnom kvaratičnom regulatoru (QR) za CSC-STATCOM. U ovom rau, CSC-STATCOM zasnovan na QR-u izajniran je za povećanje stabilnosti voporučnog energetskog sustava s va motora. Prvo su opisani postupak moeliranja te upravljački sustav zasnovan na QR-u za CSC-STATCOM. Nakon toga, prikazan je utjecaj prestavljene sheme na ispitni sustav uz prisutnost različitih poremećaja. Proveivost prestavljenog pristupa je prikazana kroz MATAB simulacije čiji rezultati prikazuju poboljšanje u prijelaznoj stabilnosti energetskog sustava s CSC-STATCOM-om. Takožer, u ovom rau je prikazana veća robusnost i efikasnost CSC-STATCOM "shunt" FACTS urežaja u onosu na SVC & VSC-STATCOM. Ključne riječi: CSC, EAC (kriterij jenakih površina), FACTS, QR, STATCOM. 1 INTRODUCTION The continuous enhancement of electrical loas ue to the moernization of the society results in transmission structure to be operate near to their stability restrictions. So the renovation of urban an rural power network becomes necessary. Due to governmental, financial an green climate reasons, it is not always possible to construct new transmission lines to relieve the power system stability problem at the existing overloae transmission lines. As a result, the utility inustry is facing the challenge of efficient utilization of the existing AC transmission lines in power system networks. So transient stability, voltage regulation, amping oscillations etc. are the most important operating issues that electrical engineers are facing uring power-transfer at high levels. In above power quality problems, transient stability is the one of the most important key factor uring powertransfer at high levels. Accoring to the literature, transient stability of a power system is its ability to maintain synchronous operation of the machines when subjecte to a large isturbance [1]. While the generator excitation system can maintain excitation control but it is not aequate to sustain the stability of power system ue to faults or overloaing near to the generator terminals [2]. Therefore researchers are working on this problem long time to fin the solution. These solutions are such as using wie-area measurement signals [3], phasor measurement unit [4] an flexible AC transmission system etc. In these

2 solutions, one of the powerful methos for enhancing the transient stability is to use flexible AC transmission system (FACTS) evices [5-8]. Even though the prime objective of shunt FACTS evices (SVC, STATCOM) is to maintain bus voltage by absorbing (or injecting) reactive power, they are also competent of improving the system transient stability by iminishing (or increasing) the capability of power transfer when the machine angle ecreases (increases), which is accomplishe by operating the shunt FACTS evices in inuctive (capacitive) moe. In many cite research papers [2, 9-11], the ifferent types of these evices an with ifferent control techniques are use for improving transient stability. Among these evices, the STATCOM is valuable for enhancement stability an frequency stabilization ue to the rapi output response, lower harmonics, superior control stability an small size etc. [8, 12, 13]. By their inverter configuration, basic Type of STATCOM topology can be realize by either a current-source converter (CSC) or a voltagesource converter (VSC) [13-17]. But recent research confirms several merits of CSC base STATCOM over VSC base STATCOM [18-2]. These avantages are high converter reliability, quick starting, inherent short-circuit protection, the output current of the converter is irectly controlle an in low switching frequency this reuces the filtering requirements compare with the case of a VSC. Therefore CSC base STATCOM is very useful in power system rather than VSC base STATCOM in many cases. Presently the most use techniques for controller esign of FACTS evices are the Proportional Integration (PI), PID controller [21], pole placement an linear quaratic regulator (QR) [22]. But QR an pole placement algorithms give quicker response in comparison to PI & PID algorithm an QR is the optimal theory of pole placement metho an escribes the optimal pole location base on two cost function [23]. So QR metho has better performance among these methos. The main contribution of this paper is the application of QR base CSC-STATCOM for transient stability improvement of power system by injecting (or absorbing) reactive power. In this paper, the propose QR controller base CSC-STATCOM is use in Two area power system with ynamic loa uner serious isturbance conitions (three phase fault or heavy loaing) to enhancement of transient stability stuies an observe impact of the CSC- STATCOM on electromechanical oscillations an transmission capacity. More ones, the resulting outcomes from the propose algorithm base CSC-STATCOM are compare to that obtaine from the other shunt FACTS evices (SVC & VSC base STATCOM) which are use in previous works [24, 25]. The rest of paper is prepare as follows. Section- 2 iscusses about the circuit moeling & QR controller esigning of CSC base STATCOM. A two-area two-machine power system is escribe with a CSC- STATCOM evice in Section-3. Simulation results of the test system with & without CSC base STATCOM for severe contingency are shown in Section-4, to improve the transient stability of the system. Comparison among the performance of ifferent shunt FACTS evices such as SVC, VSC-STATCOM an CSC-STATCOM is also presente in Section-4. Finally, Section-5 conclues this paper. 2 MATHEMATICA MODEING OF QR BASED CSC-STATCOM 2.1 CSC base STATCOM moel To verify the response of the CSC-STATCOM on ynamic performance, the mathematical moeling an control strategy of a CSC base STATCOM are presente. So in the esign of controller for CSC base STATCOM, the state space equations from the CSC base STATCOM circuit is introuce. To minimize the complexity of mathematical calculation, the theory of q transformation of currents has been applie in this circuit, which makes the an q components as inepenent parameters. Fig. 1 shows the circuit iagram of a typical CSC base STAT- COM. Fig. 1. The representation of CSC base STATCOM Where i SR, i SS, i ST v CR, v CS, v CT v R, v S, v T I c R c c line current; voltages across the filter capacitors; line voltages; c-sie current; internal resistance of the c-link inuctor (converter switching an conuction losses); C R smoothing inuctor (c-link); filter capacitance; inuctance of the line reactor; resistance of the line reactor

3 The basic mathematical equations of the CSC base STATCOM have been erive from the literature [2]. Therefore, only brief etails of the primary equations for CSC-STATCOM are given here for the reaers convenience. Base on the equivalent circuit of CSC-STATCOM as shown in Fig.1, the ifferential equations for the system can be achieve, which are erive in the abc frame an then transforme into the synchronous q frame using q transformation metho [26]. t I c = R c c I c 3 2 c M V 3 2 c M q V q (1) t I = R I + ωi q 1 E n + 1 V (2) t I q = ωi R I q + 1 V q (3) t V = 1 C I + ωv q + 1 C M I c (4) t V q = 1 C I q ωv + 1 C M qi c (5) In above ifferential equations M an M q are the two input variables. Two output variables are I c an I q. Here, ω is the rotation frequency of the system an this is equal to the nominal frequency of the system voltage. I & I q are the -axis & q-axis components of the line current. M & M q are -axis & q-axis components of the system moulating signal (m), respectively. Here M = m cos θ an M q = m sin θ (where θ is the phase angle of converter output current). E & E q are irect & quarature axis of the system voltage. Here E is taken as the RMS value of the system voltage an E q is taken as a zero. V & V q are the -axis & q-axis components of the voltage across filter capacitor, respectively. Equation (1) is shown that controller for CSC base STATCOM has nonlinearity characteristic. So this nonlinear property can be remove by accurately moeling of CSC base STATCOM. From equations (1)-(5), it can be seen that nonlinear property in the CSC-STATCOM moel is ue to the part of I c. This nonlinear property is remove with the help of active power balance equation. Here, it has been assume that the power loss in the switches an resistance R c is ignore an the turns ratio of the shunt transformer is n : 1. After using power balance equation an mathematical calculation, nonlinear characteristic is remove from the equation (1). Finally the equation is obtaine below: ( ) I 2 2R c ( ) t c = I 2 3E c c c n I (6) In the equation (6) state variable (I c ) is replace by the state variable (Ic 2 ), to make the ynamic equation linear. Finally the resulting better ynamic an robust moel of the CSC-SATACOM in matrix form can be erive as: (i c ) 2 i t i q v c = v cq 2R c c 3E c n R 1 ω o ω o R 1 1 C ω o 1 C ω o 1 C 1 C ] + I iq [ Ii 1 E (i c ) 2 i i q v c v cq + Above moeling of CSC base STATCOM is written in the form of moern control methos i.e. State-space representation. For state-space moeling of the system, section 2.2 has been consiere. 2.2 QR controller Design inear Quaratic Regulator (QR) theory is no oubt one of the most basic control system esign methos. QR algorithm is the optimal theory of pole placement metho an picks the best possible pole location base on the two cost functions. This metho fins the optimal feeback gain matrix that reuces the cost function. One way of representing the quaratic cost function in mathematics for QR formulation is below: J = x T Qxt + (7) u T Rut (8) Here Q an R are the symmetric, non-negative efinite weighting matrices. In the ynamic moeling of system, State-space equations involve three types of variables: state variables (x), input (u) an output (y) variables with isturbance (e). So comparing (7) with the stanar state-space representation i.e. ẋ = Ax + Bu + F e (9) where the system matrices as: y = Cx (1) x = [ I 2 c I I q V V q ] T ; u = [ Ii I iq ] T e = E ; y = [ I 2 c I q ] T

4 B = A = 1 c 1 c 2R c c 3E c R 1 ω ω R 1 1 c ω 1 c ω ; C = 1 1 T 1 ; F = Equations (9) & (1) represent five system states, two control inputs an two control outputs. Where, x is the state vector, u is the input vector, A is the basis matrix, B is the input matrix, e is isturbance input. Now in the presence of isturbance the control equation can be formulate as: u = K x + J y ref + N e (11) Then the state equation of close loop is moifie as ẋ = (A B K) x + J y ref + B N e + F e (12) Where K is the state-feeback matrix, N is the feeback matrix for the isturbance input, y ref is the reference input, an J is a iagonal matrix which is use to obtain the unity steay-state gain. The matrix N shoul be esigne in such a way that the output y shoul be minimally influence by the isturbance e. This objective can be achieve by making: lim C(s I A + B s K) 1 (B N + F ) = & ẋ = Therefore J & N values are foun out from a mathematical calculation for tracking the reference output value (y ref ) by the system output value (y). For computation of these values, two equations are use such as: an. J = [C ( (A B K) 1 ) B] 1 N = [C ( A + B K) 1 B] 1 [C ( A + B K) 1 F ] Here y ref can be written as below: [ ] I 2 y ref = c(ref) I q(ref) In orer to, reuce the cost function (performance inex) an to achieve the best value of gain matrices K, following two equations are use. K = R 1 B T P (13) A T P + P A P BR 1 B T P + Q = (14) Equation (14) is also calle the algebraic riccati equation [27]. The final configuration of the propose QR base CSC-STATCOM is shown in Fig. 2. Fig. 2. Control Structure of QR base CSC-STATCOM 3 TWO-AREA POWER SYSTEM WITH CSC- STATCOM FACTS DEVICE In orer to observe the performance of propose QR controller in the previous section, a two-area two-machine power system with a CSC-STATCOM is consiere, The CSC-STATCOM is connecte at bus b through a long transmission system as shown in Fig. 3. Figure 3(b) represents the equivalent circuit of test system without CSC- STATCOM. The active power flows from area 1 to area 2. Figure 3(c) represents the equivalent circuit of the test system with a CSC-STATCOM, where CSC-STATCOM is use as shunt current source evice. The ynamic moel of the machine, with a CSC- STATCOM, can be written in the ifferential algebraic equation form as follows: δ = ω (15) ω = 1 M [P m P eo P csc e ] (16) Here ω is the rotor spee, δ is the rotor angle, P m is the mechanical input power of generator, the output electrical power without CSC-STATCOM is represents by P eo an M is the moment of inertia of the rotor. Equation (16) is also calle as swing equation. The aitional factor of the output electrical power of generator from a CSC- STATCOM is Pe csc in the swing equation. From Fig. 3(b), output of generator (P eo ) is P eo = E 1V bo X 1 sin(δ θ bo ) = E 1E 2 X 1 + X 2 sin(δ) (17) Where V bo an θ bo are voltage magnitue an angle at bus b in the absence of CSC-STATCOM, which are compute as follows: [ ] θ bo = tan 1 X 2 E 1 sin δ (18) X 2 E 1 cos δ + X 1 E 2

5 ( ) X2 E 1 cos(δ θ bo ) + X 1 E 2 cos θ bo V bo = X 1 + X 2 (19) For calculation of Pe csc, Fig. 3(c) is consiere an assume that CSC-STATCOM is working in capacitive moe. The injecte current from CSC-STATCOM to test system can be written as: I csc = I csc (θ bo 9 o ) (2) (I csc ). In Fig. 3(c), the electrical output power Pe csc of machine ue to a CSC-STATCOM, can be expresse as: P csc e = E 1V b X 1 sin(δ θ b ) (23) Finally, using equations (22) & (23) the total electrical output (P e ) of machine with CSC-STATCOM can be written as P e = P eo + P csc e P e = P eo + X 1X 2 E 1 (X 1 + X 2 )X 1 I csc sin(δ θ b ) (24) All above equations are represente for the capacitive moe of CSC-STATCOM. For the inuctive moe of operation negative value of I csc can be substitute in equations (2), (22) & (24) in place of positive I csc. With the help of equation (16), the power-angle curve of the test system can be rawn for stability analysis as shown in Fig. 4. Fig. 3. A two-area two-machine power system with CSC- STATCOM; (a) A single line iagram; (b) Simplifie moel of the test system without CSC-STATCOM; (c) Simplifie moel of the test system with a CSC-STATCOM as a current injection evice In Fig. 3(c), the magnitue (V b ) an angle (θ b ) of voltage at bus b can be compute as: [ ] θ b = tan 1 X 2 E 1 sin δ (21) X 2 E 1 cos δ + X 1 E 2 ( ) X2 E 1 cos(δ θ bo ) + X 1 E 2 cos θ bo V b = X 1 ( + X 2 ) (22) X1 X 2 + I csc X 1 + X 2 From equation (22), it can be sai that the voltage magnitue of bus b (V b ) epens on the STATCOM current Fig. 4. Power-Angle characteristic of the test system with a CSC-STATCOM The power-angle (P δ) curve of the test system without a CSC-STATCOM is represente by curve A (also calle prefault conition) in Fig. 4. Here the mechanical input is P m, electrical output is P e an initial angle is δ. When a fault occurs, P e suenly ecreases an the operation shifts from point a to point b at curve B an thus the machine starts accelerating from point b to point c, where accelerating power (P a ) is positive. Here accelerating power (P a ) is the ifference between mechanical input (P m ) & electrical output (P e ) power. At fault clearing, P e suenly increase an the area a-b-c--a represents the accelerating area A a as efine in equation (25). If the CSC-STATCOM operates in a capacitive moe (at fault clearing), P e increases to point e at curve C (also calle postfault conition). At this time P a is negative. Thus the machine starts ecelerating but its angle continues to increase from point e to the point f until reaches a maximum

6 Fig. 5. The single line iagram of the test-system moel for transient stability stuy of two power plants (P1 & P2) allowable value δ m at point f, for system stability. The area e-f-g--e represents the ecelerating area A as efine in equation (25). From previous literature [1], equal area criterion for stability of the system can be written as: δc δ ( Pm Pe f ) δm δ = (Pe p P m ) δ A a = A δ c (25) This equation is generate from Fig. 4, where δ c is critical clearing angle. P p e is an electrical output for post-fault conition. P f e is an electrical output uring fault conition. From Fig. 4, it is seen that for capacitive moe of operation (I csc > ), the P δ curve is not only lifte up but also isplace towar right an that enues more ecelerating area an hence higher stability limit. Now in the following section transient stability of two-area two-machine power system is analyze using the propose QR base controller with CSC-STATCOM. 4 SIMUATION RESUTS 4.1 Power system uner stuy: In this section, two-area power system is consiere as test system for stuy. For this type of test system, a 5-kV transmission system with two hyraulic power plants P 1 (machine-1) & P 2 (machine-2) connecte through 7-km long transmission line is taken as shown in Fig. 5. Rating of first power generation plant (P 1 ) is 13.8 kv/1 MVA, which is use as P V generator bus type. The electrical output of the secon power plant (P 2 ) is 5 MVA, which is use as a swing bus for balancing the power. One 5 MW large resistive loa is connecte near the plant P 2 as shown in Fig. 5. To maintain the synchronism of plants (i.e. machines 1 & 2) an improve the transient stability of the test system after isturbances (faults or heavy loaing), a QR base CSC-STATCOM is connecte at the mi-point of transmission line (at bus B2). Achieve maximum efficiency; CSC-STATCOM is connecte at the mipoint of transmission line, as per [28]. The two hyraulic generating units are assemble with a turbine-governor set an excitation system, as explaine in [1]. Power oscillation amping (POD) unit is not use with shunt FACTS evice. All the ata require for this test system moel are mentione in Appenix A. The impact of the QR controller base CSC- STATCOM has been observe for maintaining the system stability through MATAB/SIMUINK. Severe contingencies such as short-circuit fault an instant loaing, are consiere. 4.2 Case I-Short-Circuit Fault: A three-phase fault is create at near bus B1 at t =.1 s an is cleare at.23 s. The impact of system with & without CSC base STATCOM, ue to this isturbance are shown in Figs. 6 to 11. Simulations are carrie out for 8 s to observe the nature of transients. From Figs. 6 & 7, it is observe that the system without CSC-STATCOM is unstable even after the clearance of the fault. But the same system with QR base CSC-STATCOM is restore an stable after the clearance of the fault as observe from Figs. 8 to 11. Synchronism between two machines M1 & M2 is also maintaine as shown in Figs. 9 & 1. CCT is efine as the maximal fault uration for which the system remains transiently stable [1]. The critical clearing time (CCT) of fault

7 Fig. 6. Test system response without CSC-STATCOM for a three phase fault (Case-I). (a) Positive sequence voltages at ifferent buses B1, B2 & B3 (b) Power flow at bus B2 Fig. 8. Test-system response with CSC-STATCOM for a three phase fault (Case-I). (a) Positive sequence voltages at ifferent buses B1, B2 & B3 (b) Power flow at bus B2 Fig. 9. Rotor angles ifference of machines M1 & M2 for case-i Fig. 7. System response without CSC-STATCOM for Case- I (a) Difference between Rotor angles of machines M1 & M2 (b) w1 & w2 spees of machine M1 & M2 respectively (c)terminal voltages Vt1 & Vt2 of generators M1 & M2 respectively is also foun out for the test system stability by simulation. The fault time is increase to fin the critical stability margin, thus CCT is obtaine. CCT of the fault for system with & without CSC-STATCOM are 286 ms an 222 ms respectively, as shown in Table-1. It is observe that CCT of fault is also increase ue to the impact of QR base CSC-STATCOM. 4.3 Case II-arge oaing: For heavy loaing case, a large loa (1 MW/5 Mvar) is connecte at near bus B1 (i.e. at near plant P 1 ) in Fig. 5. This loaing occurs uring time perio.1 s to.5 s. Due to this isturbance, the simulation results of test system with an without CSC-STATCOM are shown in Figs. 12 to 17. Clearly, Fig. 1. Machine spees w1 & w2 with CSC-STATCOM for case-i the system becomes unstable in the absence of CSC- STATCOM ue to this isturbance as in Figs. 12 & 15. But system with CSC-STATCOM is stable as observe in Figs. 14 to 17. Figure 17 also shows the amount of reactive power injecte or absorbe by CSC-STATCOM

8 Fig. 11. For case-i (a) terminal voltages Vt1 & Vt2 of generators M1 & M2 with CSC-STATCOM respectively (b) reactive power inject (or absorb) by CSC-STATCOM to the test system for maintaining the system stability. The CCT for the system with & without CSC-STATCOM are 585 ms & 442 ms respectively, which are provie in Table 1. Clearly, CCT for test system is better ue to QR base CSC-STATCOM. Hence the performance of CSC-STATCOM is satisfactory in this case also. Fig. 13. System response without CSC-STATCOM for Case-II (a) Difference between Rotor angles of machines M1 & M2 (b) w1 & w2 spees of machine M1 & M2 respectively (c)terminal voltages Vt1 & Vt2 of generators M1 & M2 respectively Fig. 14. Spees w1 & w2 for machines M1 & M2 respectively for case-ii Fig. 12. The test system response without CSC-STATCOM for a heavy loaing (Case-II). (a) Positive sequence voltages at ifferent buses B1, B2 & B3. (b) Power flow at bus B2 4.4 Case III-A comparative stuy: In orer to emonstrate the robust performance of the propose scheme for improving the transient stability of the system, outcomes from the propose QR base CSC- STATCOM are compare to that obtaine from the other shunt FACTS evices such as SVC an VSC base STAT- COM which have been reporte in [24], [25]. It has been assume that the test system is same for all shunt FACTS Fig. 15. Rotor angle ifference of machines M1 & M2 for system with an without CSC-STATCOM in case-ii

9 Fig. 16. The test system response with CSC-STATCOM for a heavy loaing (Case-II). (a) Positive sequence voltages at ifferent buses B1, B2 & B3. (b) Power flow at bus B2 Table 1. CCT of isturbances for the test system stability with ifferent shunt FACTS evices Critical Clearing S. No. FACTS evices Time (CCT) Case-I Case-II Case-III Without CSC-STATCOM With CSC-STATCOM Without CSC-STATCOM With CSC-STATCOM With SVC With VSC-STATCOM With CSC-STATCOM 1 ms 222 ms 1 ms 286 ms 1 ms 442 ms 1 ms 585 ms 1 ms 237 ms 1 ms 24 ms 1 ms 286 ms Fig. 17. For case-ii (a) terminal voltages Vt1 & Vt2 of generators M1 & M2 with CSC-STATCOM respectively (b) reactive power inject (or absorb) by CSC-STATCOM Fig. 18. System response with ifferent shunt FACTS evices (CSC-STATCOM, VSC-STATCOM & SVC) for Case- III (a) Difference between Rotor angles of machines M1 & M2 (b) spee ifference of machines M1 & M2 evices an all shunt FACTS evices have the same rating (2 Mvar). To check the impact of these shunt FACTS evices on the test system with three phase fault conition, simulation results with these shunt FACTS evices are compare in Fig. 18. The three phase fault uration is.1 s to.2 s. CCT for the system with ifferent shunt FACTS evices are shown in Table-1. If three-phase fault uration is increase i.e. from.1 s to.24 s, then system with SVC becomes unstable. This is shown in Fig. 19. Waveforms show that CSC-STATCOM is more effective an robust than that of other shunt FACTS evices (SVC & VSC-STATCOM) in terms of oscillation amping, settling time, CCT an transient stability of the test-system in Figs. 18 & CONCUSIONS In this paper, a two cost function base QR controller for the better input-output response of CSC-STATCOM is propose in orer to enhance the transient stability of the power system uner various kins of isturbances. The QR base state feeback control technique is formulate an applie to the CSC-STATCOM. The ynamic moeling of CSC base STATCOM is presente. The QR base CSC-STATCOM moel is mae inepenent of the operating point by applying the power balance equation. With the help of QR base CSC-STATCOM, transient stability of a two-area two-machine power system is improve an CCT of isturbances are also increase. The propose scheme is simulate an verifie on MATAB platform. This paper also compares the performance of CSC-

10 A.3 Parameters of shunt FACTS evices: SVC:- System nominal voltage (-): 5 kv; f : 5 Hz; K p = 3; K i = 5; V ref = 1. VSC-STATCOM:- System nominal voltage (-): 5 kv; DC link nominal voltage: 4 kv; DC link capacitance:.375 µf; f: 5 Hz; K p = 5; K i = 1; V ref = 1. CSC-STATCOM:- System nominal voltage (-): 5 kv; V b = E ; R c =.1 Ω; c = 4 mh; C f = 4 µf; R =.3 Ω; = 2 mh; ω = 314; V ref = 1. Fig. 19. System response with 3-phase fault for.1s to.24s in Case-III (a) Difference between Rotor angles of machines M1 & M2 (b) spee ifference of machines M1 & M2 STATCOM with other shunt FACTS evices such as SVC & VSC-STATCOM in terms of oscillation amping, CCT an transient stability of two-area power system. It is observe that the CSC-STATCOM is more reliable an effective in comparison to these other FACTS evices. Hence, CSC base STATCOM can be regare as an alternative FACTS evice to that of other shunt FACTS evices i.e. SVC & VSC-STATCOM. APPENDIX A Parameters for various components use in the test system configuration of Fig. 5. (All parameters are in pu unless specifie otherwise): A.1 For generator of plant (P 1 & P 2 ): V G = 13.8 kv; R s =.3; f = 5 Hz; X = 1.35; X =.296; X =.252; X q =.5; X q =.243; T = 1.1 s; T =.53 s; H = 3.7 s. Where R s is stator wining resistance of generators; V G is generator voltage (-), f is frequency; X is synchronous reactance of generators; X & X are the transient an sub-transient reactance of generators in the irect-axis; X q & X q are the transient an sub-transient reactance of generators in the quarature-axis; T & T are the transient an subtransient open-circuit time constant; H the inertia constant of machine. A.2 For Excitation System of machines (M1 & M2): Regulator gain an time constant (Ka & Ta): 2,.1 s; Gain an time constant of exciter (Ke & Te): 1, S; Damping filter gain an time constant (Kf & Tf):.1,.1 s; Upper an lower limit of the regulator output:, 7. REFERENCES [1] Prabha Kunur, "Power system stability an control, McGraw-Hill, [2] M. A. Abio, "Power system stability enhancement using FACTS controllers: a review," The Arabian Journal for Science an Engineering, Volume 34, Number-1B,pp , April 29. [3] C.X. Dou, S.. Guo, X.Z. Zhang, "Improvement of transient stability for power systems using wiearea measurement signals," Electrical Engineering, springer Publishing, vol. 91, pp , 29. [4] X. D. iu, Y. i, Z. J. iu, Z. G. Huang, Y. Q. Miao, Q. Jun, Q. Y. Jiang, an W. H. Chen, "A novel fast transient stability preiction metho base on pmu," in Power & Energy Society General Meeting, pp. 1-5, 29. [5] R. J. Nelson, J. Bian, D. G. Ramey, T. A. emak, T. R. Rietman, an J. E. Hill, "Transient stability enhancement with FACTS controllers," in Proceeings of the 6th International Conference on AC an DC Power Transmission, pp , May [6] H. S. Hosseini, an A. Ajami, "Transient Stability Enhancement of AC Transmission System using STATCOM", IEEE TENCON 2, Vol. 3, pp , Oct. 22. [7] Y.. Tan an Y. Wang,"A robust nonlinear excitation an SMES controller for transient stabilization", International Journal of Electrical Power & Energy Systems, vol. 26, no. 5, pp [8] M. H. Haque,"Improvement of first swing stability limit by utilizing full benefit of shunt facts evices", IEEE Trans. Power Syst., vol. 19, no. 4, pp , 24. [9] N.C. Sahoo, B.K. Panigrahi, P.K. Dash an G. Pana, Multivariable nonlinear control of STATCOM for

11 synchronous generator stabilization, International Journal of Electrical Power & Energy Systems, Volume 26, Issue 1, Pages 37 48, January 24. [1] H. Tsai, C. Chu an S. ee, "Passivity-base Nonlinear STATCOM Controller Design for Improving Transient Stability of Power Systems", Proc. of IEEE/PES Transmission an Distribution Conference & Exhibition: Asia an Pacific Dalian, China, 25. [11] Arinam Chakraborty, Shravana K. Musunuri, Anurag K. Srivastava, an Anil K. Konabathini, Integrating STATCOM an Battery Energy Storage System for Power System Transient Stability: A Review an Application, Avances in Power Electronics, Hinawi Publishing, vol. 212, Article ID 6761, 12 pages, 212. [12] Tan, Y., "Analysis of line compensation by shuntconnecte FACTS controllers: a comparison between SVC an STATCOM," IEEE Power Engineering Review, vol. 19, no.8, pp , [13] B. Singh, R. Saha, A. Chanra an K. Al-Haa, "Static synchronous compensators (STATCOM): A review", IET Power Electron., vol. 2, no. 4, pp , 29. [14] N. G. Hingorani an. Gyugyi, Unerstaning FACTS: Concepts an Technology of Flexible ac Transmission Systems, IEEE Press, New York, [15] B. Han an S. Moon, "Static synchronous compensator using thyristor PWM current source inverter", IEEE Transactions Power Delivery, vol. 15, pp.1285, 2. [16] Saneep Gupta, R. K. Tripathi, "Voltage Stability Improvement in Power Systems using FACTS Controllers: State-of-the- Art Review", IEEE International Conference on Power, Control an Embee Systems (ICPCES), pp.1-8, 21. [17] H.F. Bilgin, M. Ermis, Current source converter base STATCOM: Operating principles, esign an fiel performance, Electric Power Systems Research, Volume 81, Issue 2, Pages , February 211. [18] D. Shen an P. W. ehn "Moeling, analysis, an control of a current source inverter-base STAT- COM", IEEE Transactions Power Delivery, vol. 17, pp.248, 22. [19] M. Kazearni an Y. Ye "Comparative evaluation of three-phase PWM voltage- an current-source converter topologies in FACTS applications", Proc. IEEE Power Eng. Soc. Summer Meeting, vol. 1, pp.473, 22. [2] Y. Ye, M. Kazerani, Victor H. Quintana, "Current- Source Converter Base STATCOM: Moeling an Control", IEEE Transactions on Power Delivery, vol.2, no.2, April 25. [21] Y. Ni,. Jiao, S. Chen an B. Zhang, "Application of a Nonlinear PID Controller on STATCOM with a Differential Tracker," International Conference on Energy Management an Power Delivery, EMPD-98, New York, USA, pp , [22], "Two-Area Power System Stability Improvement using a Robust Controller base CSC-STATCOM", Acta Polytechnica hungarica, vol. 11/7, pp , 214. [23] P. Rao, M.. Crow an Z. P. Yang, "STATCOM control for power system voltage control applications, IEEE Transactions Power Delivery, vol. 15, no. 4, pp , 2. [24] G. Sybille an P. Giroux, "Simulation of FACTS controllers using the MATAB power system blockset an Hypersim real-time simulator", IEEE Power Eng. Soc. Panel Session on Digital Simulations of FACTS an Custom Power Controllers, Winter Meeting, p.p , January 22. [25] Sihartha Pana an Ramnarayan N. Patel, Improving Power System Transient Stability with an Off Centre ocation of Shunt FACTS Devices, Journal of Electrical Engineering, vol. 57, No. 6, , 26. [26] C. Schauer an H. Mehta "Vector analysis an control of avance static VAR compensators", IEE Proceeings of Generation, Transmission an Distribution, vol. 14, pp.299, [27] Katsuhiko Ogata, "Moern Control Engineering", 5th Eition, Prentice Hall, 21. [28] B. T. Ooi, M. Kazerani, R. Marceau, Z. Wolanski, F. D. Galiana, D. McGillis an G. Joos "Mipoint sitting of facts evices in transmission lines", IEEE Trans. Power Del., vol. 12, no. 4, pp , 1997.

12 Saneep Gupta receive the B.Tech. an M.E. egrees in Electrical Engineering in 26 an 29, respectively. Currently, he is an associate professor at Rajasthan Institute of Engineering & Technology Jaipur. He is also a research scholar at Motilal Nehru National Institute of Technology Allahaba-2114, Inia. His areas of interest in research are Application of artificial intelligence to power system control esign, FACTS evice, Power Electronics an stability of power system. He has been author an co-author of many papers publishe in journals an presente at the national an international conferences. Ramesh Kumar Tripathi was born in Allahaba on August 1, He receive the B.E. (Hons.) egree in electrical engineering from Regional Engineering College, Durgapur, University of Burwan (W.B.), Inia, in 1989 an the M. Tech. Degree in microelectronics from Institute of Technology, Banaras Hinu University, Varanasi, Inia, in He receive Ph.D. egree in power electronics from Inian Institute of Technology, Kanpur, Inia, in 22. Currently he is Prof. & Hea in the Department of Electrical Engineering, Motilal Nehru N.I.T. Allahaba, Inia. His research interests are Power Electronics, Reactive Power Control, Switch Moe Rectifiers, Power Quality, Active Power Filters an Virtual Instrumentation. He has been author an coauthor of many papers publishe in journals an presente at the national an international conferences. AUTHORS ADDRESSES Saneep Gupta Department of Electrical Engineering, Rajasthan Institute of Engineering & Technology Jaipur - 335, INDIA guptavilab@gmail.com Prof. Ramesh K. Tripathi Department of Electrical Engineering, Motilal Nehru National Institute of Technology Allahaba , INDIA rktripathi@mnnit.ac.in