Synchronous Voltage Reversal control of TCSC– impact on SSR conditions

Hailian Xie Lennart Ängquist

EME/ETS, Royal Institute of Technology, Stockholm

Series compensation

capacitor bank inserted in series with transmission line

aims to increase the power transfer capacity of high-voltage transmission line

fixed capacitor bank may cause a Torsional Interaction Sub-Synchronous Resonance (TI-SSR) problem with thermal power generators

Thyristor Controlled Series Capacitor (TCSC) may solve this problem

EME/ETS, Royal Institute of Technology, Stockholm

TCSC main circuit and generic waveforms

EME/ETS, Royal Institute of Technology, Stockholm

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-2

0

2

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-5

0

5

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-50

0

50

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-40

-20

0

Line current

Valve current

Capacitor voltage

Apparent reactance

About this paper

describes the laboratory setup of a TCSC model with the SVR (Synchronous Voltage Reversal) control scheme

presents the result from an investigation concerning the impact of the SVR controlled TCSC on SSR in the real-time simulator

EME/ETS, Royal Institute of Technology, Stockholm

Diagram of the real-time simulator

EME/ETS, Royal Institute of Technology, Stockholm

Infinite

bus u2

Source 1 impedanceu1

Line FixedImpedance capacitor

TCSC inductance

TCSC capacitor

Thyristor valve

SVR Control scheme

EME/ETS, Royal Institute of Technology, Stockholm

2

c

t

iL

iv

uc SVR idea: control capacitor voltage zero-crossing instant

TCSC capacitor

SVR boost control system overview

EME/ETS, Royal Institute of Technology, Stockholm

PLL

Boost controller

uc (measured)

kBref + kBm _

pulses

-XC0 Re

Im

SVR trig pulse

generation

TCSC inductance

Thyristor valve

il (measured)

Apparent Z evaluation

Phasor estimation

Method to analyze the system damping

EME/ETS, Royal Institute of Technology, Stockholm

Kel

DelTel

iL LPfilter

Calculate the electrical

torque

In DSP In Matlab

Calculate the spring constant and damping

coefficient

Generate system voltage

u1Control

modulation

Re(ΔTel)Im(ΔTel)

Electrical damping curve (1)

system with fixed series compensation

EME/ETS, Royal Institute of Technology, Stockholm

10 15 20 25 30 35 40 45-15

-10

-5

0

5Del & Kel with fixed series compensation

De

l [p

u t

rq/p

u s

pd

]

10 15 20 25 30 35 40 45-2

-1

0

1

2

3

mech freq [Hz]

Ke

l [p

u t

rq/r

ad

]

Electrical damping curve (2)

system with SVR controlled TCSC

EME/ETS, Royal Institute of Technology, Stockholm

10 15 20 25 30 35 40 45-6

-4

-2

0

2

4SVR control, no PLL, no boost control

De

l [p

u t

rq/p

u s

pd

]

10 15 20 25 30 35 40 45-2

-1

0

1

2

3

mech freq [Hz]

Ke

l [p

u t

rq/r

ad

] KB=1.2KB=1.72

Electrical damping curve (3)

Comparison between SVR and control

EME/ETS, Royal Institute of Technology, Stockholm

10 15 20 25 30 35 40 45-6

-4

-2

0

2

4KB=1.2, no PLL, no boost control

De

l [p

u t

rq/p

u s

pd

]

10 15 20 25 30 35 40 45-2

-1

0

1

2

3

mech freq [Hz]

Ke

l [p

u t

rq/r

ad

] SVR controlbeta control

Electrical damping curve (4)

SVR control with different parameters

EME/ETS, Royal Institute of Technology, Stockholm

10 15 20 25 30 35 40 45-8

-6

-4

-2

0

2

4SVR, KB=1.72, medium boost control with different PLL speed

De

l [p

u t

rq/p

u s

pd

]

10 15 20 25 30 35 40 45-2

0

2

4

mech freq [Hz]

Ke

l [p

u t

rq/r

ad

]

s lowmediumfast

Conclusions

at low boost factor, SVR controlled TCSC can provide much better damping than conventional control scheme that controls the firing angle directly

the damping characteristic of SVR controlled TCSC with respect to SSR is almost independent of the boost factor

the tuning of the boost controller and PLL makes no critical difference on the TCSC SSR behavior

EME/ETS, Royal Institute of Technology, Stockholm

Thank you!Thank you!

EME/ETS, Royal Institute of Technology, Stockholm