Using a TCSC for Line Power Scheduling and System Oscillation Damping Small Signal and Transient Stability Studies Nelson Martins - CEPEL Herminio Pinto - CEPEL John J. Paserba - Mitsubishi Electric Products, Inc.
Paper Outline TCSC control aspects reviewed Tutorial example (Full data provided) Two line power scheduling strategies Design of power oscillation damping controller Potential control problems during line outages Transient stability results 2
Small Power System with TCSC 2 3 1000 MW 1 P1-2 P2-3 4 P2-4 P4-3 3
TCSC Control System Diagram Power System x cont TCSC Controls PI Controller F 1 (s) x ref + Σ PI (s) POD Controller B PI + Σ B 2-4 + B POD F 2 (s) POD (s) x inp 4
TCSC Controls x cont PI Controller B max Parallel Line Status x ref + Σ Ki + Kp s B min + POD Controller Logic ON/OFF Protection + Σ B PI B POD + B max Series Susceptance B min B 2-4 x inp stw 1 + stw 1 + sat 1 + st n K stab Washout Lead-Lag Gain Ki = 5, Kp = 0.5 in all cases x cont = P 2-4 for Constant Line Power Strategy x cont = P 2-4 + P 2-1 for Constant Angle Strategy B max = 5 B min = 2.5 = 0.1 5
TCSC at Fixed Impedance Mode 70 0-70 0. 5. 10. 15. 20. 25. 30. Dominant Mode λ = +0.305 ±j j 6.126 6
POD Controller Design POD Controller design is here based on Nyquist Plots of a chosen Open Loop Transfer Function (OLTF) Generator speed (ω) is chosen as the POD controller input Local bus frequency could be used No need for phase compensation 7
POD Controller Design 0.0 020 2. 0.0 011 5.9 rad/s 1. 5.9 rad/s 5.0 rad/s A 0.0 002-0.0 007 6.12 rad/s Z A 0. -1. 6.12 rad/s -1 9.0 rad/s Z -0.0 016 6.5 rad/s -2. 6.5 rad/s -0.0 025-0.0 045-0.0 030-0.0 015 0.0 000 Real -3. -4.5-3. -1.5 0. Real Nyquist Plot of OLTF POD Controller Nyquist Plot of OLTF * POD (s) ω (s) s 3.0 1 + s 3.0 +1000 B POD (s) Washout Gain 8
TCSC with POD Controller 0.016 0.012 P 1-2 0.008 P 2-3 0.004 P2-4 0.000 0. 5. 10. 15. 20. 25. 30. -0.004 Dominant Mode λ = -0.890 ±j j 5.822 9
Root Locus for Changes in Gain of POD Controller 8 K = 1500 K = 300 Imaginary K = 500 4 K = 0-1.5-1 -0.5 0 0.5 Real 0 10
TCSC Line Power Scheduling Strategies Constant Line Power Keeps the power flow in line 2-42 4 at a specified value Constant Angle Line 2-42 4 absorbs any changes in generator power Keeps the steady-state state flows at parallel fixed impedance paths at constant level 11
TCSC with POD and Constant Line Power Controllers 0.016 0.012 P 1-2 0.008 P 2-3 0.004 P 2-4 Keeps the power flow in line 2-4 at a specified value 0.000 0. 5. 10. 15. 20. 25. 30. -0.004 Dominant Modes: λ = -0.889 ±j j 5.771 and λ = -0.123 12
TCSC with POD and Constant Angle Controllers 0.016 0.012 P 1-2 0.008 P 2-4 0.004 P 2-3 0.000 0. 5. 10. 15. 20. 25. 30. Keeps the power flow in the parallel path at constant level -0.004 Dominant Modes: λ = -0.849 ±j j 5.829 and λ = -0.123 13
Step Disturbance in TCSC Line Power Order 0.010 P 2-4 0.005 0.000 P 1-2 -0.005-0.010 P 2-3 0 5 10 15 20 25 30 Dominant Mode λ = -0.123 14
Line Outage Condition (Small Signal and Transient Stability) For non-linear simulation: t = 0.5 s -> Short circuit in line 2-3 t = 0.6 s -> Fault clearance by line tripping t = 0.6 s -> Reject of one gen. unit (200 MW) 800 MW 1 P1-2 2 P2-3 = zero 4 3 P2-4 P4-3 P1-2 = P2-4 = P4-3, neglecting losses 15
Line Outage Condition (Small Signal Stability Results) PI-Controller = ON POD Controller = ON Serious Control Problem Dominant Mode: λ = 0 0.04 Ι 1-2 0.02 0.00 0. 5. 10. 15. 20. V 2-0.02 V 4-0.04 16
Line Outage Condition (Small Signal Stability Results) PI-Controller = OFF POD Controller = ON System Stable Dominant Mode: λ = -2.41 ±j 3.64 0.015 0.012 P 2-4 0.009 P 1-2 0.006 0.003 0.000 0. 5. 10. 15. 20. 25. 30. 17
Transient Stability Results Const. Line Power and POD Controllers are active TCSC output limiter is active (B min, B max ) System Very Poorly Damped 5.0 1000 4.5 4.0 B TCSC 800 P 2-4 3.5 3.0 600 2.5 0. 2. 4. 6. 8. 10. 400 0. 2. 4. 6. 8. 10. Fault Clearance by line tripping and one generator unit drop ( t = 0.6 s ) Short circuit in line 2-3 ( t = 0.5 s ) 18
Transient Stability Results Const. Line Power and POD Controllers are active Both TCSC limiters are active System Performance Still Inadequate 5.0 1000 4.5 4.0 B TCSC 800 P 2-4 3.5 3.0 600 2.5 0. 2. 4. 6. 8. 10. 400 0. 2. 4. 6. 8. 10. Fault Clearance by line tripping and one generator unit drop ( t = 0.6 s ) Short circuit in line 2-3 ( t = 0.5 s ) 19
Transient Stability Results PI-Controller channel turned off by protection logics when line 2-3 is tripped System Highly Damped 5.0 1000 4.5 4.0 800 P 2-4 3.5 3.0 B TCSC 600 2.5 0. 2. 4. 6. 8. 10. 400 0. 2. 4. 6. 8. 10. Fault Clearance by line tripping and one generator unit drop ( t = 0.6 s ) Short circuit in line 2-3 ( t = 0.5 s ) 20
Concluding Remarks Benefits gained by using modal analysis and frequency response in addition to transient stability TCSC effective for line power schedulling and system oscillation damping Some additional protection, e.g. power flow controller blocking, may be needed when certain contingencies occur or when the controller is saturating 21