Optimal location of shunt FACT devices for Power flow control in power System

Optimal location of shunt FACT devices for Power flow control in power System

Ravi Kumar Hada1, Sarfaraz Nawaz2 M.Tech. Scholar, SKIT, Jaipur, Rajasthan, India

Assistant Professor, Department of Electrical, SKIT, Jaipur, Rajasthan, India

Abstract Power flow control, in an existing long transmission line, plays a vital role in Power System area. In this the shunt connected compensation (STATCOM) based FACTS device for the control of voltage and the power flow in long distance transmission line. The proposed device is used in different locations such as sending end of the transmission line, middle and receiving end of the transmission line. The PWM control strategy is used to generate the firing pulses of the controller circuit. Simulations were carried out using MATLAB Simulink environment. The suitable location and the performance of the proposed model were examined. Based on a voltage-sourced converter, the STATCOM regulates system voltage by absorbing or generating reactive power. The simulation results reveals that the reactive power generated is better at the middle of the transmission line when compared with the other ends of the transmission line and also the voltage is controlled at the middle of the line. Henceforth the location of STATCOM is optimum when connected at the middle of the line.

Keywords FACTS device, STATCOM, PWM technique, MATLAB Simulink.

1. INTRODUCTION

   In Present scenario the applications of the power electronics devices in power systems are very much augmented. It is an urgent need to control the power flow, in a long distance transmission line. The FACTS devices are introduced in the power system transmission for the reduction of the transmission line losses, Increases Power System Stability and also to increase the transfer capability. STATCOM is VSC based controller to regulate the voltage by varying the reactive power in a long transmission line. Tan Y.L., et al[1] have demonstrated the effectiveness of SVC and STATCOM of same rating for the enhancement of power flow. Xia Jiang Xinghao Fang Chow et al [2] have focused on modelling converter-based controllers when two or more VSCs are coupled to a dc link (e.g., unified power-flow controller (UPFC), interline power-flow controller, and a generalized unified power-flow controller) and in their approach they allowed efficient implementation of various VSC operating limits, where one or more VSCs are loaded to their rated capacity. Chandrakar, V.K. et al [3] have investigated the optimal location of shunt FACTS devices in transmission line for highest possible benefit under normal condition and also they considered three different line models namely, line impedance model, reactance model and pi() model. Bebic, J.Z.[4] have presented two such topologies, the first one

   consists of a shunt connected controllable source of reactive power, and two series connected voltage-sourced converters – one on each side of the shunt device which is named as "hybrid power flow controllers", or HPFC. Johnson, B.K.[5] has presented an overview of how series connected and combined series/shunt connected FACTS controllers are studied in an AC system. Shankaralingappa, C.B.[6] has achieved the optimum required rating of series and shunt flexible ac transmission systems controllers for EHVAC long transmission lines by computing `optimum compensation requirement' (OCR) for different loading conditions. Shakib,

   A.D. [7] has defined a sensitivity analysis, which is used to determine the area on which the FACTS device has significant influence, for the detection of sensor nodes and then only this limited area is included in the Optimal Power Flow control. Salemnia, A. et al [8] have proposed the concept of using remote signals acquired through PMU to damp SSR. K.R. Padiyar et al[9] have considered a series passive compensation and shunt active compensation provided by a static synchronous compensator (STATCOM) connected at the electrical center of the transmission line to minimize the effects of SSR. Prabhu, N. et al [10] has investigated the sub synchronous resonance (SSR) characteristics of the system and proposed a novel method for the extraction of sub synchronous component of line current using filter. Zarghami, M.et al [11] has discussed a novel approach for damping interarea oscillations in a large power network using multiple STATCOMs. Yap, E.M. et al[12] have focused on the effective utilization of a flexible alternating current transmission system (FACTS) device called unified power flow controller (UPFC) for power flow control and also demonstrated the use of the latest power system analysis toolbox (PSAT) package for network analysis of alternative means of improving existing transmission capability. Y u Liu Bhattacharya, S. et al[13] have designed a controller in which an optimal combination modulation strategy is used, which leads to some challenges in designing the controller, such as extra switching and the balancing of individual dc capacitor voltages. Larki, F. et al [14] have presented a new approach for identification of optimal locations of STATCOM and SVC and also simulated case studies conducted on Kouzestan power networks in Iran based on the proposed techniques. Albasri, F.A.et al[15] have investigated a comparative study of the performance of distance relays for transmission lines compensated by shunt connected flexible ac transmission system (FACTS) controllers.

   In this paper performance strategy were conducted on STATCOM at different locations such as sending end, middle and the receiving end of the long distance transmission line. In every part of the location the power flow is tested with and without compensation strategy. In this paper also shows the effect of STATCOM on voltages of system buses and power flows in both steady state and abnormal conditions. The simulink model of the three bus system is developed and tested using MATLAB Simulink environment.

2. OPERATING PRINCIPLE

   A STATCOM is comparable to a Synchronous Condenser (or Compensator) which can supply variable reactive power and regulate the voltage of the bus where it is connected. The equivalent circuit of a Synchronous Condenser (SC) is shown in Fig.1, which shows a variable AC voltage source (E) whose magnitude is controlled by adjusting the field current. Neglecting losses, the phase angle () difference between the generated voltage (E) and the bus voltage (V) can be assumed to be zero. By varying the magnitude of E, the reactive current supplied by SC can be varied. When E = V, the reactive current output is zero. When E > V, the SC acts as a capacitor whereas when E < V, the SC acts as an inductor. When = 0, the reactive current drawn (Ir) is given by

   (1)

   Fig.1 A Synchronous Condenser Fig.2 A Single Phase STATCOM

   A STATCOM (previously called as static condenser (STATCON)) has a similar equivalent circuit as that of a SC. The AC voltage is directly proportional to the DC voltage (Vdc) across the capacitor (see Fig.2 which shows the circuit for a single phase STATCOM). If an energy source (a battery or a rectifier) is present on the DC side, the voltage Vdc can be held constant. The self-commutated switchesT1 and T2 (based on say GTOs) are switched on and off once in a cycle. The conduction period of each switch is 180 and care has to be taken to see that T1 is off when T2 is on and vice versa. The diodes D1 and D2 enable the conduction of the current in the reverse direction. The charge on the capacitors ensures that the diodes are reverse biased. The voltage waveform across PN is shown in Fig.3. The voltage VPN = Vdc/2 when T1 is conducting (T is off) and VPN = -Vdc/2 when T2 is conducting (and T1 is off).

   Fig.3 The waveform of VPN

3. MODELING OF STATCOM

   Based on the operating principle of the STATCOM, the equivalent circuit can be derived, which is given in Fig.4. In the derivation, it is assumed that (a) harmonics generated by the STATCOM are neglected; (b) the system as well as the STATCOM are three phase balanced.

   Then the STATCOM can be equivalently represented by a controllable fundamental frequency positive sequence voltage source Vsh. In principle, the STATCOM output voltage can be regulated such that the reactive power of the STATCOM can be changed.

   Fig.4 STATCOM Equivalent Circuit

   According to the equivalent circuit of the STATCOM shown in Fig.4, suppose Vsh = Vshsh , Vi = Vi i , then the power flow constraint of the STATCOM are:

   (2)

   (3)

   Where

   .

   The operating constraint of the STATCOM is the active power exchange via the DC link as described by:

   (4)

   Where

4. SIMULATION MODEL

   (5)

   the "natural" power flow on the transmission line is 951.4 MW from bus B1 to B3. STATCOM has a rating of +/- 100MVA. This STATCOM is a phasor model of a typical three-level PWM STATCOM.

   Fig.5 explains about the circuit diagram without compensation. In this circuit the power is directly measured in the 600km long transmission line at the three stages like B1,

   Here we considered a three bus Power system which consists of two 500-KV equivalents generators, respectively 3000 MVA and 2500 MVA, connected by a 600-km long transmission line. When the STATCOM is not in operation,

   B2 and B3 and also tabulated the result in table1. Fig.6 explains about the circuit diagram when STATCOM is connected at the Middle of the long transmission line. Similarly the connections are made when the STATCOM is connected at the sending end and receiving end of the long transmission line.

   Fig.5 Simulink Model of Power System without compensation

   Fig.6 Simulink Model of Power System with STATCOM at Middle

5. SIMULATION RESULTS

   To understand the Effect of presence of STATCOM in system, on system parameters, typical cases we have carried out by simulation analysis of the system. The results are generated by MATLAB outputs shown on respective cases. The results of cases are tabulated, analyzed and compared which clearly shows the Effect of the STATCOM under various conditions. The cases are as under.

   1. Effect on Power flows at B1, B2 and B3 in Steady State

      980

      960

      940

      920

      Real Power in MW

      900

      880

      860

      840

      820

      800

      780

      Plot of Real Power/Time

      								B1 B2 B3

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.9 Real Power at B1, B2 & B3 when STATCOM is at Sending End

      Operation (Case-1)

   2. Effect on Power flows at B1, B2 and B3 in HV and LV Condition (Case-2)

   3. Effect on Power flows at B1, B2 and B3 in Increasing Load Condition (Case-3)

   4. Effect on Voltages of System buses at B1, B2 and B3 for steady state, HV, LV and increasing load condition (Case-4)

   5. Effect on Power flows due to Optimal Location of STATCOM (Case-5)

   100

   50

   Reactive Power in MVAr

   0

   -50

   -100

   Plot of Reactive Power/Time

   B1 B2

   B3

   1. Case-1

      -150

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.7 and Fig.8 highlights the real and reactive power control at the three stages when the STATCOM is not connected i.e. without compensation.

      Fig.10 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End

   2. Case-2

      Fig.11 and Fig.12 highlights the real and reactive power

      960

      940

      920

      900

      Plot of Real Power/Time

      control at the three stages when the STATCOM is not connected i.e. without compensation in HV Condition. Fig.13

      										B1 B2 B3

      and Fig.14 highlights the real and reactive power control at the three stages when the STATCOM is not connected i.e. without compensation in LV Condition.

      Real Power in MW

      880

      										B1 B2 B3

      1060

      Plot of Real Power/Time

      860

      840

      820

      800

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Fig.7 Real Power at B1, B2 & B3 without compensation

      Plot of Reactive Power/Time

      										B1 B2 B3

      80

      60

      1040

      1020

      1000

      Real Power in MW

      980

      960

      940

      920

      900

      880

      40

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Fig.11 Real Power at B1, B2 & B3 without compensation for High voltage

      Reactive Power in MVAr

      20 condition

      									B1 B2
      									B3

      0 100

      Plot of Reactive Power/Time

      -20

      -40

      -60

      -80

      -100

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Fig.8 Reactive Power at B1, B2 & B3 without compensation

      80

      60

      40

      Reactive Power in MVAr

      20

      0

      -20

      -40

      -60

      -80

      Fig.9 and Fig.10 highlights the real and reactive power control at the three stages when the STATCOM is connected at

      -100

      -120

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Sending End i.e. with compensation.

      Fig.12 Reactive Power at B1, B2 & B3 without compensation for High

      voltage condition

      880

      860

      840

      Real Power in MW

      820

      800

      780

      760

      740

      Plot of Real Power/Time

      900

      880

      860

      840

      Real Power in MW

      820

      800

      780

      760

      740

      							B1 B2 B3

      Plot of Real Power/Time

      										B1 B2 B3

      720

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      720

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.13 Real Power at B1, B2 & B3 without compensation for Low voltage condition

      Plot of Reactive Power/Time

      										B1 B2 B3

      80

      60

      40

      Reactive Power in MVAr

      20

      0

      -20

      -40

      -60

      -80

      Fig.17 Real Power at B1, B2 & B3 when STATCOM is at Sending End for low voltage Condition

      Plot of Reactive Power/Time

      100

      B1 B2

      80 B3

      60

      40

      Reactive Power in MVAr

      20

      0

      -20

      -40

      -60

      -80

      -100

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      -100

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.14 Reactive Power at B1, B2 & B3 without compensation for Low voltage condition

      Fig.15 and Fig.16 highlights the real and reactive power control at the three stages when the STATCOM is connected at Sending End i.e. with compensation in HV Condition. Fig.17 and Fig.18 highlights the real and reactive power control at the three stages when the STATCOM is connected at Sending End i.e. with compensation in LV Condition.

      Fig.18 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End for Low voltage Condition

   3. Case-3

      Fig.19 and Fig.20 highlights the real and reactive power control at the three stages when the STATCOM is not connected i.e. without compensation in Increasing Load Condition.

      Plot of Real Power/Time

      											B1 B2 B3

      1000

      1060

      1040

      1020

      1000

      Real Power in MW

      980

      960

      940

      920

      900

      Plot of Real Power/Time

      B1 B2

      B3 950

      Real Power in MW

      900

      850

      800

      750

      880

      860

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Fig.19 Real Power at B1, B2 & B3 without compensation for Increasing Load

      Plot of Reactive Power/Time

      										B1 B2 B3

      60

      Fig.15 Real Power at B1, B2 & B3 when STATCOM is at Sending End for high voltage Condition

      Plot of Reactive Power/Time

      80

      60

      40

      20

      Reactive Power in MVAr

      0

      -20

      -40

      -60

      40

      20

      Reactive Power in MVAr

      0

      -20

      -40

      -60

      -80

      -100

      -120

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      -80

      -100

      -120

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.16 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End for high voltage Condition

      Fig.20 Reactive Power at B1, B2 & B3 without compensation for Increasing Load

      Fig.21 and Fig.22 highlights the real and reactive power control at the three stages when the STATCOM is connected

      at Sending End i.e. with compensation in Increasing Load Condition.

      			B2
      			B1
      			B3

      0.975

      Plot of Voltage/Time

      1050

      1000

      950

      Real Power in MW

      900

      850

      800

      750

      Plot of Real Power/Time

      0.97

      0.965

      Voltages in pu

      0.96

      0.955

      0.95

      0.945

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      700

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.25 Voltages of system bus B1, B2 and B3 without compensation for Low Voltage Condition

      Fig.21 Real Power at B1, B2 & B3 when STATCOM is at sending end for

      			B2
      			B3
      			B1

      Increasing Load Condition 1

      Plot of Reactive Power/Time

      Plot of Voltage/Time

      80

      60

      40

      20

      Reactive Power in MVAr

      0

      -20

      -40

      -60

      -80

      -100

      0.995

      Voltages in pu

      0.99

      0.985

      0.98

      0.975

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      -120

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.22 Reactive Power at B1, B2 & B3 when STATCOM is at sending end for Increasing Load Condition

   4. Case-4

      Fig.23 to Fig.26 highlights the Voltages at the three stages when the STATCOM is not connected i.e. without

      Fig.26 Voltages of system bus B1, B2 and B3 without compensation for Increasing Load Condition

      Fig.27 to Fig.30 highlights the voltages at the three stages when the STATCOM is connected at Sending End i.e. with compensation in Steady State, HV, LV and Increasing Load Condition respectively.

      compensation in Steady State, HV, LV and Increasing Load Condition respectively.

      Plot of Voltage/Time

      		B2
      			B1

      1.025

      1.02

      1.015

      Voltages in pu

      1.01

      1.005

      1.035

      1.03

      1.025

      1.02

      Voltages in pu

      1.015

      1.01

      1.005

      1

      0.995

      0.99

      Plot of Voltage/Time

      1 B3

      0.985

      	B2
      	B1
      	B3

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      0.995

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Fig.27 Voltages of system bus B1, B2 and B3 with compensation for Steady state Condition

      Fig.23 Voltages of system bus B1, B2 and B3 without compensation for

      Steady state Condition

      Plot of Voltage/Time

      1.07

      Plot of Voltage/Time

      			B2
      			B1
      			B3

      1.08

      1.075

      1.07

      Voltages in pu

      1.065

      1.06

      1.055

      1.05

      1.045

      0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

      Time in sec

      Fig.24 Voltages of system bus B1, B2 and B3 without compensation for High Voltage Condition

      1.065

      	B2
      	B1
      	B3

      1.06

      1.055

      Voltages in pu

      1.05

      1.045

      1.04

      1.035

      1.03

      1.025

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.28 Voltages of system bus B1, B2 and B3 with compensation for High voltage Condition

      Plot of Voltage/Time

      		B2
      		B1
      		B3

      1

      960

      Plot of Real Power/Time

      0.99

      0.98

      Voltages in pu

      0.97

      0.96

      0.95

      0.94

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.29 Voltages of system bus B1, B2 and B3 with compensation for Low voltage Condition

      940

      920

      900

      Real Power in MW

      880

      860

      840

      820

      800

      780

      								B1 B2 B3

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.33 Real Power at B1, B2 & B3 when STATCOM is at Middle

      Plot of Reactive Power/Time

      1.03

      1.02

      1.01

      Voltages in pu

      1

      0.99

      Plot of Voltage/Time

      100

      B1 B2 B3

      50

      Reactive Power in MVAr

      0

      -50

      -100

      	B2
      	B3
      	B1

      0.98

      0.97

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      -150

      0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

      Time in sec

      Fig.34 Reactive Power at B1, B2 & B3 when STATCOM is at Middle

      Fig.30 Voltages of system bus B1, B2 and B3 with compensation for Increasing Load Condition

   5. Case-5

   Fig.35 and Fig.36 highlights the real and reactive power control at the three stages when the STATCOM is connected at Receiving End.

   Fig.31 and Fig.32 highlights the real and reactive power control at the three stages when the STATCOM is connected at Sending End.

   980

   960

   940

   920

   Plot of Real Power/Time

   B1 B2 B3

   980

   960

   940

   920

   Real Power in MW

   900

   880

   860

   840

   								B1 B2 B3

   Plot of Real Power/Time

   Real Power in MW

   900

   880

   860

   840

   820

   800

   0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

   Time in sec

   Fig.35 Real Power at B1, B2 & B3 when STATCOM is at Receiving End

   Plot of Reactive Power/Time

   820

   800

   780

   0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

   Time in sec

   Fig.31 Real Power at B1, B2 & B3 when STATCOM is at Sending End

   Plot of Reactive Power/Time

   150

   B1 B2 B3

   100

   50

   B1 B2 B3

   100

   50

   Reactive Power in MVAr

   0

   -50

   0

   Reactive Power in MVAr

   -50

   -100

   -150

   0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

   Time in sec

   -100

   -150

   0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

   Time in sec

   Fig.32 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End

   Fig.33 and Fig.34 highlights the real and reactive power control at the three stages when the STATCOM is connected at Middle.

   Fig.36 Reactive Power at B1, B2 & B3 when STATCOM is at Receiving End

6. CONCLUSION

The vital role of shunt FACTS devices, which are connected in long distance transmission lines, are to improve the power transfer capability and also to control the power flow in the power system network. In this proposed work STATCOM is

employed as a shunt FACTS device. STATCOM is connected at the various locations such as sending end, middle and receiving end of the transmission line. The results were obtained with and without compensation. The simulation results reveals that the reactive power generated is better at the middle of the transmission line when compared with the other ends of the transmission line and also the voltage is controlled at the middle of the line. So, the location of STATCOM is optimum when connected at the middle of the line.

IEEE Conference on TENCON 2009, pp 1-6, Jan.2009.

1. Zarghami, M. Crow, M.L. Damping inter-area oscillations in power systems by STATCOMs, 40th North American Symposium 2008, pp 1-6, 978-1- 4244-4283-6, Sept 2008.

   REFERENCES [13]			Yu Liu Bhattacharya, S. Wenchao Song Huang, A.Q.
   			Control strategy for cascade multilevel inverter
   [1]	Tan, Y.L., Analysis of line compensation by shunt-		based STATCOM with optimal combination
   	connected FACTS controllers: a comparison between		modulation, IEEE Conference on Power Electronics
   	SVC and STATCOM, IEEE Transactions on Power		Specialists, PESC 2008, pp 4812-4818, June 2008.
   	Engineering Review, Vol.19, pp 57-58, Aug 1999.	[14]	Larki, F. Kelk, H.M. Pishvaei, M. Johar, A.
   [2]	Xia Jiang Xinghao Fang Chow, J.H. Edris, A.-A.		Joorabian, M. Optimal Location of STATCOM and
   	Uzunovic, E. Parisi, M. Hopkins, L. A Novel		SVC Based on Contingency Voltage Stability by
   	Approach for Modeling Voltage-Sourced Converter-		Using Continuation Power Flow: Case Studies of
   	Based FACTS Controllers, IEEE Transactions on		Khouzestan Power Networks in Iran, Second
   	Power Delivery, Vol.23(4), pp 2591-2598, Oct 2008.		International Conferenceon Computer and Electrical
   [3]	Chandrakar, V.K. Kothari, A.G. Optimal location		Engineering, ICCEE 2009, pp 179-183, Dec 2009.
   	for line compensation by shunt connected FACTS	[15]	Albasri, F.A. Sidhu, T.S. Varma, R.K. Performance
   	controller, The Fifth International IEEE Conference		Comparison of Distance Protection Schemes for
   	on Power Electronics and Drive Systems, Vol 1, pp		Shunt-FACTS Compensated Transmission Lines,
   	151-156, Nov 2003.		IEEE Transactions on Power Delivery, Vol.22(4), pp
   [4]	Bebic, J.Z. Lehn, P.W. Iravani, M.R. The hybrid		2116-2125, Oct 2007.
   	power flow controller – a new concept for flexible
   	AC transmission, IEEE Power Engineering Society		TABLE I

2. Yap, E.M. Al-Dabbagh, M. Thum, P.C. Applications of FACTS Controller for Improving Power Transmission Capabiity, IEEE Conference on TENCON 2005, pp 1-6, Nov 2005.

General Meeting, DOI-10.1109/PES.2006.1708944, Oct 2006.

1. Johnson, B.K. How series and combined multiterminal controllers FACTS controllers function in an AC transmission system, IEEE Power Engineering Society General Meeting, Vol.2, pp 1265-1267, June 2004.

2. Shankaralingappa, C.B. Jangamashetti, S.H. FACTS Controllers to Improve Voltage Profile and Enhancement of Line Loadability in EHV Long Transmission Lines, International IEEE Conference on POWERCON, pp 1-5, Oct 2008.

3. Shakib, A.D. Balzer, G. Optimal location and control of shunt FACTS for transmission of renewable energy in large power systems, 15th IEEE Mediterranean Electrotechnical Conference, MELECON 2010, pp 890-895, Apr 2010.

4. Salemnia, A. Khederzadeh, M. Ghorbani, A. Mitigation of subsynchronous oscillations by 48- pulse VSC STATCOM using remote signal, IEEE Transactions on Power Tech, pp 1-7, June 2009.

5. K.R. Padiyar N. Prabhu Design and performance evaluation of subsynchronous damping controller with STATCOM, IEEE Transactions on Power Delivery, Vol.21(3), pp 1398-1405, July 2006.

6. Prabhu, N. Janaki, M. Thirumalaivasan, R. Damping of subsynchronous resonance by subsynchronous current injector with STATCOM,

COMPARISON OF P & Q