Abouelabbas Ghanaim, Georg Frey

1. Faculty of Technology Electrical Engineering Dept. Modeling and Simulation of Ethernet based Networked Control Systems (NCS) using Colored Petri Nets (CPN) Abouelabbas Ghanaim, Georg Frey

2. Outline • Networked Control Systems Definition (NCS) • Colored Petri Net Introduction • Proposed CPN based NCS Model • Simulation and Results • Expected Future Work

3. Networked Control System (NCS) τca τsc Tank filling example A Networked Control System (NCS): is a control system wherein the control loops are closed through a real-time network. The defining feature of an NCS is that control and feedback signals are exchanged among the system's components in the form of information packages through a network. τca is a network time delay from controller to actuator τsc is a network time delay from sensor to controller

4. NCS system Block Diagram Actual Value Set Value τca Controller Plant Actuator + - - τca:Network time delay from controller to actuator Sensor Client Side Server Side LAN τsc:Network time delay from sensor to controller τsc Blockdiagram זּca: Network time delay from controller to actuator can be called: Forward Network Delay זּsc : Network time delay from sensor to controller can be called: Backward Network Delay

5. Definition Petri Nets p2 t2 t1 p1 p3 t3 • Petri Net: is a formal, graphical and executable technique for the specification and analysis of concurrent, discrete-event dynamic systems. • In a formal way, a PN is a tuple: • P is a finite set of Places. • T is a finite set of Transitions. • A is a finite set of Arcs • M is a initial marking set of Token

6. Formal Definition of Colored Petri Nets • In a formal way, a CPN is a tuple is a tuple: • P is a finite set of Places. • T is a finite set of Transitions. • A is a finite set of Arcs. • is a finite set of non-empty types, also called colored sets • C is a color function. It is defined from P into “token” • E is an arc expression function. It is defined from A in to expressions. • G is a guard function. It is defined from T into Boolean expressions • M is an initialization Marking [Guard] t1 e2 e1 Color set c2 Color set c1 p1 p2 Initail marking m1

7. Colored Petri Nets Features • Colored Petri Net: is a graphical oriented modeling language developed for systems in which communication, synchronization and resource sharing play an important role. • CP-nets combine the strengths of ordinary Petri nets with the strengths of a high-level programming language. • Petri nets provide the primitives for process interaction, while the programming language provides the primitives for the definition of data types and the manipulations of data values.

8. Cpn Tools Software • CPN Tools is one of the most well-known GUI Software for editing, simulating and analyzing of Hierarchal Colored Petri Nets (HCPN) from the University of Aarhus, Department of Computer Science – Daimi, Denmark. http://wiki.daimi.au.dk/cpntools/cpntools.wiki • A CPN model consists of a set of modules (pages) which each contains a network of places, transitions and arcs. • The modules interact with each other through a set of well-defined interfaces, in a similar way as known from many modern programming languages. • The graphical representation makes it easy to see the basic structure of a complex CPN model, i.e., understand how the individual processes interact with each other.

9. Colored Petri Net (CPN) based NCS Model Model characteristic: • Modeling well-known automation components in the automation market • Component based model structure with I/O Configuration tables through tokens. • Actual data flow through tokens represent Modbus frames encapsulated in Ethernet data packages. • Model for realistic program execution. • Cyclic and event based execution capability. • Ethernet client server network model. Model Layout

10. Model Structure • System : contains main outline of the system by cloning the individual ready-made automation Components sub-models. • PLC: consists of two parts • Processor • Send/Receive (Ethernet interface) • I/O module: with built in send/receive (Ethernet interface) • Ethernet Switch • Plant

11. Model from Inside Model Main Page

12. Simulation CPN model used in Simulation זּca: Network time delay from controller to actuator can be called: Write Delay זּsc : Network time delay from sensor to controller can be called: Read Dealy

13. Simulation and Results • Simulation Setup: • Ramp integer input Signal with 1ms time Intervals • IO module scan cycle with 2ms • PLC scan cycle with 10ms • IO scanner cycle update with 17ms

14. Results • The delay patterns are periodic and we can determine this period accurately using frequency analysis techniques. • The delay patterns are a function of the cycle times and the time skew between these scan cycles. • In most cases the read and write delay are periodic with anti-phase that makes the total delay almost constant.

15. Present versus Future Work  • CPN-based Network Control System model with well-known Automation components was constructed with cyclical execution. • Simulation Results of the delays in the NCS model indicate periodicity in the delay patterns witch can accurately determined by frequency analysis techniques. • The model will be modified to adapt for closed loop interactions and simple control algorithms. • Comparison of the CPN models a typical first order plus dead time case study. • Modeling the delays as a Hidden Markov chains models with a system identification overcome the limitations of the CPN for continuous process models that need real number manipulations.

16. My poster in ETFA2008 Thank you for attention! Welcome for Questions! and Open Discussion

17. PLC with IO Scanner module

18. Ethernet Switch

19. IO Module with IO adaptor

20. Ramp signal Input Process