Impact of Signal Delay Attack on Voltage Control for Electrified - - PowerPoint PPT Presentation

Impact of Signal Delay Attack on Voltage Control for Electrified Railways

Hoang Hai Nguyen1 Rui Tan1 David K. Y. Yau1,2

1Advanced Digital Sciences Center (Singapore),

University of Illinois at Urbana-Champaign

2Singapore University of Technology and Design

Motivation

3rd largest cluster of cyber-physical attacks 2014 Moscow derailment

• Cyber-attacks on industrial control systems

– Dragonfly, Stuxnet – 11 transportation intrusions in 2013

• Voltage control in traction power systems

– Cybernated, safety-critical – Voltage drop before Moscow derailment

3 largest cluster of cyber-physical attacks [U.S. CERT / ICS-CERT, 2013]

https://ics-cert.us-cert.gov/sites/default/files/ICS-CERT_Monitor_April-June2013_3.pdf

2014 Moscow derailment [Image from USNews]

Background

• AC traction power systems

– Up to 50 kV – Substations connected to utility grid or dedicated power grid

• Large voltage fluctuations

– Trains: moving loads – De-accelerating trains: moving generators – Train shift between sections causes step change – Train shift between sections causes step change

Background

• AC traction power systems

– Up to 50 kV – Substations connected to utility grid or dedicated power grid

• Large voltage fluctuations

– Trains: moving loads – De-accelerating trains: moving generators – Train shift between sections causes step change – Train shift between sections causes step change

Generators or transformers Voltage sensors Centralized controller Comm. networks Traction power grid Changing power consumption of trains

Voltage Control

• State-space model for multi-bus power grid

x[k] ≈ x[k −1]+Cu[k]+B(q[k]−q[k −1])

Voltage Control

• State-space model for multi-bus power grid

x[k] ≈ x[k −1]+Cu[k]+B(q[k]−q[k −1])

substation voltages generator/transformer voltages substation reactive power draws

Voltage Control

• State-space model for multi-bus power grid

x[k] ≈ x[k −1]+Cu[k]+B(q[k]−q[k −1])

substation voltages generator/transformer voltages substation reactive power draws

– Maintain x at nominal x0 when q changes

Voltage Control

• State-space model for multi-bus power grid

x[k] ≈ x[k −1]+Cu[k]+B(q[k]−q[k −1])

substation voltages generator/transformer voltages substation reactive power draws

– Maintain x at nominal x0 when q changes

• Control algorithm

– BIBO stable if 0 < α < 2 – Similar controls applied in practice

u[k]=αC−1(x0 − x[k])

Signal Delay Attack

Generators or transformers Voltage sensors Centralized controller Comm. networks Traction power grid Changing power consumption of trains

• Controller uses old voltage measurements

u[k] = αC-1(x0 – x[k – τ])

sensors networks

Signal Delay Attack

Generators or transformers Voltage sensors Centralized controller Comm. networks Traction power grid Changing power consumption of trains

• Controller uses old voltage measurements

– Network congestion, time desynchronization – Easier than data integrity attacks u[k] = αC-1(x0 – x[k – τ])

sensors networks

Impact of Attack on Stability

• System state transform

– New state transition model [ ]

] [ , , ] 1 [ , ] [ ] [ x x x x x x y − − − − − = τ n n n n L

    − I I I L L α

• G’s characteristic polynomial

– Stable: All roots in unit circle of complex plane

              = ⋅ = + I I I G y G y L M M O M M M L L ] [ ] 1 [ n n

1

= + −

+

α λ λ

τ τ

Impact of Attack on Stability

• System state transform

– New state transition model [ ]

] [ , , ] 1 [ , ] [ ] [ x x x x x x y − − − − − = τ n n n n L

    − I I I L L α

• G’s characteristic polynomial

– Stable: All roots in unit circle of complex plane

              = ⋅ = + I I I G y G y L M M O M M M L L ] [ ] 1 [ n n

1

= + −

+

α λ λ

τ τ

u[n] = αC-1(x0 – x[n – τ])

Stable Region

• λτ+1 – λτ + α = 0

– No closed-form solutions – Jury test

• f α

Malicious time delay τ Stable region of

Stable Region

• λτ+1 – λτ + α = 0

– No closed-form solutions – Jury test

• f α

Malicious time delay τ Stable region of

When no attack

• Faster convergence
• Smaller fluctuation

Stable Region

• λτ+1 – λτ + α = 0

– No closed-form solutions – Jury test

• f α

Malicious time delay τ Stable region of

When no attack

• Faster convergence
• Smaller fluctuation

Trade-off btw control performance and tolerable malicious delay

An Example

Voltage α=0.2 α=0.8

• PowerWorld simulations

– 37-bus power system – 10 feeder buses under voltage control No attack

Time step k Voltage deviation (p.u.) Voltage deviation (p.u.)

τ = 2

α=0.2 α=0.8 α=0.2

Analysis Verification

• Approximations in system modeling

– Affect accuracy of stability analysis

Malicious time delay τ Stable region of α

By Jury test By simulations

Summary and Future Work

• Stability condition of voltage control under

signal delay attack

• Trade-off between

– Voltage convergence speed when no attack – Voltage convergence speed when no attack – Tolerable time delay in terms of stability

• Future work

– Other voltage control approaches – Attack mitigation