Interfacing Power System and ICT Simulators: Challenges, State...

Interfacing Power System and ICT Simulators:

Challenges, State-of-the-Art and Study Cases

Contributors:

S. C. Müller, H. Georg, J. J. Nutaro, E. Widl, Y. Deng, P. Palensky,

M. U. Awais, M. Chenine, M. Küch, H. Lin, S. Shukla, C. Wietfeld,

C. Rehtanz and M. Stifter

IEEE Power & Energy Society General Meeting 2014National Harbor, MD, USA, July 31th, 2014

IEEE Task Force on Interfacing Techniques for Simulation Tools



Motivation

Transition towards smart grids and cyber physical energy systems

Rise of wide-area monitoring, protection and control (WAMPAC) systems

Interaction of power system and ICT becomes more and more important,

but is often simplified in simulations

Involvement of many entities for reliable execution of applications

Communication (PMUs to PDC, inter/intra substation, controls,…)

IT data processing (decision making algorithms,…)

Latencies all along the ICT chain could be influential / critical

Impact on sequence of events, overlapping communication traffic

Impact on real-time performance of time-critical applications (e.g. wide-area protection systems)

Threat of cyber attacks



ICT-based WAMPAC systemsNeed for integrated analysis of power and ICT system for WAMPAC applications

• Failures in power and ICT systems can lead to critical situations in power system

operation

• mutual effects in both networks (e.g. overlapping network flows)

• real-time capability of WAMPAC applications depends on whole system behavior

• Detailed modeling of both networks is necessary for performance evaluation in order to

guarantee overall real-time requirements.



Focus of paper

Providing a first reference for power system engineers

outlining the challenges of a combined simulation of power and ICT systems

presenting the State of the Art of available solutions and research approaches

exemplifying the value and possibilities of an integrated simulation at the example

of test cases

Topic cannot be covered extensively on 8 pages

Bringing together a team of experienced research groups for focusing on the most

critical aspects from their perspective



Team

TU Dortmund University

Developers of INSPIRE co-simulator S. C. Müller, H. Georg, M. Küch, C. Rehtanz, C. Wietfeld,

Austrian Institute of Technology (AIT)

Dedicated research group on complex energy systemsand interfacing techniques

P. Palensky, E. Widl, U. Awais, M. Stifter

Virginia Tech

Developers of GECO co-simulator Y. Deng, S. Shukla, H. Lin

Oak Ridge National Laboratory

Developer of ADEVS simulator J. J. Nutaro

KTH Stockholm

Research group on real-time and hardware-in-the-loop simulation M. Chenine



Structure

I. Introduction

II. Modeling and Simulation Principles

Power Systems

Communication networks

Challenges of an integrated analysis of both domains

III. State of the Art: Interfacing power and ICT systems simulators

Simulation frameworks

Co-simulation approaches

Real-time and hardware-in-the-loop approaches

IV. Exemplary case studies

• Impact of cyber-attacks on PMU-based state estimation (using GECO simulator)

• Impact of ICT scenarios on power flow control application (using INSPIRE simulator)

V. Outlook and conclusion

VI. References



Outline

• Motivation and focus

• Team

• Modeling and simulation principles of power system and ICT simulators

• Challenges of an integrated analysis of both domains

• State-of-the-art of interfacing power and ICT systems simulators

• Simulation frameworks, co-simulation, real-time and hardware-in-the-loop simulation

• Exemplary case studies

• Impact of cyber-attacks on PMU-based state estimation (using GECO simulator)

• Impact of ICT scenarios on power flow control application (using INSPIRE simulator)



Modeling and simulation principles

• Excellent tools for distinct domains available

• Fundamental mathematics and numerical methods are available for simulating smart

power systems

• Difficulty lies in the cost of creating new models within new simulation frameworks for

hybrid systems

• Strong incentive to reuse existing simulation tools and models within tools

• Tradeoff as choice of picking two out of three options:

a. Reuse of communication and power system models within well-established simulation

packages

b. Accurate simulations of interactions between the two domains

c. Rapid execution of combined simulation




• Power System Simulation

• Continous time calculations:

• System of different algebraic equations (DAEs) governed

by fundamental physical laws

• Physical coupling & dynamic interaction of many individual components and large number

of interdependent states (e.g. all synchronous machines are coupled via network

frequency and influence each other)

• DAEs solved by numerical integration methods → physical continous time processes

simulated using discrete time steps

• Communication network simulation

• Functional modeling of hardware and software processes as sequential processing

and transmission of messages and signales

• Simulations with help of discrete sequence of events in time

• Events are localized at nodes and only affect other nodes indirectly, e.g. by delay

• Often complex processes happening at software and hardware layers modeled by

statistical models with random distributions




• Challenges of integrated analysis

• Time synchronous and deterministic execution of

• discrete event based (Communication Network)

• discrete time based (Power System)

• Object management

• Detect, link and handle related events in both domains

• Approaches for a combined analysis

• General purpose tools

• Simulation of hybrid models combining power system and

communication network domains

• Tools often lack modeling libraries, solvers and validated models

• Co-simulation

• Use specialized tools for both domains, reuse validated models

• Challenges: synchronization at runtime, lack of adequate APIs

• Hardware-in-the-loop (HIL):

• Coupling real-world hardware with a simulation tool

• Similar challenges as co-simulation, plus real time constraints



State of the Art:Interfacing power and ICT system simulations

• Simulation frameworks for interfacing simulators of both domains

i. High Level Architecture (HLA, IEEE 1516)

ii. Functional Mock-up Interface (FMI)

iii. Mosaik

iv. Ad-hoc

• Review of advanced co-simulation approaches

i. A Discrete EVent System simulator (ADEVS)

ii. Electrical Power and Communication Synchronizing Simulator (EPOCHS)

iii. Global Event-Driven Co-Simulation Framework (GECO)

iv. Integrated co-Simulation of Power and ICT systems for Real-time Evaluation (INSPIRE)

v. Other solutions and discussion

• Real-time and Hardware-in-the-Loop approaches



State of the Art:Interfacing power and ICT system simulations



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PDC1

PDC2

PDC3

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Control

Center

Exemplary case studiesCase I – Scenario Description

• Analysis of cyber-attacks on PMU-based state estimation using GECO

• Scenario:

• IEEE 39-bus 10-machine system

(New England Test System)

• Each bus 1 PMU

(reporting at 30 𝐻𝑧)

• 4 PDCs (50 𝑚𝑠 timer) and

1 Super PDC

calculating final state estimation

• Communication links in

parallel with transmission lines



Exemplary case studiesCase I – Simulation Results

i. Normal operation (only small random PMU measurement error)

ii. Link failure attack: communication link from bus 16 to 17 blocked at 𝑡 = 0.2𝑠

Due to new routing measurements arrive after Super PDC timer expires

System becomes unobservable




iii. Link saturation attack: malicious traffic injected at 𝑡 = 0.2𝑠

No immediate effect, but gradual saturation of link, from 𝑡 = 0.42𝑠 on essential

measurements have to compete with malicious traffic

State estimation still possible due to other redundant measurements




iv. Denial of Service (DoS) attack: depletion of the resources of a router by large amount of

redundant data or inquiries

System state switches between observable and unobservable



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ControlCenter

Loss oftransmission line

LastverschiebungFlexible loads

Exemplary case studiesCase II

Analysis of real-time performance of wide-area power flow control using INSPIRE

Scenario:

• Line TL0506 disconnect

after 𝑡 = 10𝑠, causing

overload of line TL0405

• “Load redispatch“ at

Substations 4 and 5

• Control Center at

Substation 39

• polling measurements

every 100𝑚𝑠

• switching loads on

demand

• 4 scenarios for the

communication network

Communication Protocol:

• IEC 61850

• Type of Messages:MMS – Type 2

• Monitoring

ACSI Service:GetDataValues

• Switching

ACSI Service:SetDataValue

• Logical Device:Bay Controller

(BBxx_BC_B1)




• Scenario 1

Reference scenario,

no counteraction



Clearance: 0,5s


• Scenario 2

Idle communication network

Message flow:

Measurements are

transmitted to Control

Center

Control Center detects

overload

Control Center schedules

load redispatch at

Substation 4 and 5

Effect

Synchronous

adjustments

Overload drops within

less than 0.5𝑠



7

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PFC 1

PFC 4

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G

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PFC 3

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20G

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G

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24PFC 2

PFC 1

PFC 4

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PFC 3

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• Scenario 3

• Simultaneous

line disconnect in the


• Message Flow as before




• Scenario 3

• Simultaneous

line disconnect in the


• Message Flow as before

• Effects:

• Routes needs to be

updated

• Traffic flow changes

• Routing protocol causes

additional delay

• Asynchronous adjustments

• Overload drops in 1.39 𝑠resp. 1.58 𝑠 (both average)




• Scenario 4

Unprioritized network traffic

Additional traffic load in the


Additional background

traffic as before

Message flow as before

Effects:

Additional delay due to

non exclusive usage of

the network

Asynchronous

adjustments

Overload drops in 1.69 𝑠resp. 1.88 𝑠 (both

average)




• Scenario 5

Modeling of distributed redispatch

in distribution grid

Transmission system control

needs realized by large number

of decentralized entities

Wireless control commands

(WiMAX, TDMA (GSM))




• Scenario 5

Modeling of distributed redispatch

in distribution grid

Transmission system control

needs realized by large number

of decentralized entities

Wireless control commands

(WiMAX, TDMA (GSM))

Effects:

Packet losses -> realized control

effect is smaller than command

Timely distribution of control

realizations instead of

simultaneous action

Delay dependent on wireless

technology



Conclusion

• Evolution of smart grids requires appropriate tools for simulating power and ICT systems

together

• Key challenges for interfacing discrete event based ICT simulators and continuous time

resp. discrete time based power system simulators

• Time synchronization

• Event handling

• Data exchange

• Various approaches available: general purpose tools, co-simulation, HIL

• Tradeoff between accuracy, execution time and ease of implementation

• Review and comparison of various state-of-the-art solutions

• Different time advance strategies, use of standardized frameworks,...

• Two case studies demonstrate capabilities of two state-of-the-art approaches as well as

necessity and value of combined simulation environments

Thank you for your Attention!



• Centralized Monitoring and Control Layer

Centralized components within the Power Systems

(e.g. centralized protection, control center, power plants, etc.)

Components at this layer cannot communicate directly

Within the simulator architecture, these components will be mapped to specialized

simulators

Layers of ICT-based power system operationCentralized and decentralized monitoring and control, interconnected by WAN



• Local Process Layer

Traffic arising within substation and field level

(e.g. local monitoring, measurements, process control, etc.)

Components at this layer can communicate directly

(e.g. using optical fibres)

Communication to other layers has to be transmitted using the

Wide-Area Communication Layer




• Wide-Area Communication Layer

Interconnecting the other layers

Providing heterogeneous communication infrastructure (wired or wireless)

Necessity of fallback solutions

(e.g. dedicated wireless broadband, cellular networks, etc.)


Interfacing Power System and ICT Simulators: Challenges, State...

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