1. Networked Control Systems Theory and Its Application
Shanbin Li, PhD student
NCS Research Group
National Laboratory of Industrial Control Technology
Zhejiang University
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

2. Networked Control Systems Theory and Its Application
Introduction
State-of-the-arts of NCS
Our results
Current focus
Future work
Summary
Questions and remarks
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

3. ZJU-NLICT-NCS Research Group By Shanbin Li
Introduction
What is networked control system? ?
Do you know the fundamentals of NCS?
Network has its positive side ,what is negative side?
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

4. Development history of control system
Analogous control system
Centralized digital control system
Decentralized control system
Fieldbus control system (FCS)
Networked control system (NCS) by Gregory C. Walsh 1998
Integrated communication and control systems (ICCS) by Ray Asok 1988
Partly Digital
Partly Analogous
Completely Distributed
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ZJU-NLICT-NCS Research Group By Shanbin Li

5. ZJU-NLICT-NCS Research Group By Shanbin Li
Introduction
Reference
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ZJU-NLICT-NCS Research Group By Shanbin Li

6. ZJU-NLICT-NCS Research Group By Shanbin Li
Definition of NCS
NCS is a completely distributed and networked real-time
feedback control system.
It is an integration of sensors, controllers (+estimators),
actuators and communication network of certain local field and
is used to provide data transmission between devices in order
that users of different sites can realize resource sharing and
coordinating manipulation.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

7. QoS-parameters of network considered in the control loop
Time-delay
It varies with network topology, network protocol, network load, network bandwidth and package size
Its value may be bounded, unbounded, time-varying, constant and random
Packet losses
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ZJU-NLICT-NCS Research Group By Shanbin Li

8. ZJU-NLICT-NCS Research Group By Shanbin Li
Normal Sampling
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ZJU-NLICT-NCS Research Group By Shanbin Li

9. Vacant Sampling and Packet loss
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ZJU-NLICT-NCS Research Group By Shanbin Li

10. State-of-the-arts of NCS
Methodology One: From the view of guaranteeing network QoS. This is a scheduling methodology.
Methodology Two: From the view of guaranteeing system QoP. This is a control methodology.
Methodology Three: QoS and QoP co-consideration This is an integrated scheduling and control methodology.
Quality of Performance
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

11. Methodology One: Scheduling Part
Revise network MAC protocol
Walsh ,Ye, Bushnell introduce an novel protocol TOD (Try-Once-
Discard) and scheduling method MEF (Maximum-Error-First) based on the MATI (Maximal-Allowable-Transfer-Interval) which is denoted as  .
In TOD, the node with the greatest weighted error from its last report value
will win the competition for the network resource .If a data packet fails to win the competition for network access, it is discarded and new data is used next time.
Again, the MATI constraint ensures at least one such transmission every  .
This protocol can be realized by using CAN.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

12. Methodology One: Scheduling Part
P-CSMA-CA:
Level 1: highest priority, time-critical aperiodic data that is burst and cannot bear any loss, retransmission is required when the formal transmission is unsuccessful ;
Level 2: time-critical periodic that can tolerate some loss, data that has not been sent will be discarded
Level 3: lowest priority, consists of non-critical data which requires data integrity.Retransmission is implemented. If collisions occur, a random back-off is adopted .
Revise network MAC protocol
Ye, Walsh, Bushnell 2000 introduce a scheduling protocol P-CSMA/CA (Prioritized-CSMA-CA) based on IEEE wireless standard. For the first time, they proposed and validated several new algorithms, a constant penalty, an estimated error order and a lag first order for dynamically scheduling the traffic of wireless networked control systems.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

13. Methodology One: Scheduling Part
Sampling time scheduling
Hong, 1995 presented a scheduling method of network bandwidth allocation and sampling period decision for multi-loop NCSs in virtue of the notion “window”, namely the service window of each transmission data in network.
Hong & Kim 2000 extended this method to random delay networks such as CAN
Kim, Kwon, and Park 1996, 1998 enhanced the concept of sampling time scheduling to develop another algorithm for multi-dimensional NCS.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

14. Methodology One: Scheduling Part
Shaping
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ZJU-NLICT-NCS Research Group By Shanbin Li

15. Methodology Two: Control Part
Augmented deterministic discrete-time method
Halevi and Ray，1988 proposed a method to control a linear plant over periodic delay network
Liou and Ray，1990 introduced a method to analyze the systems with multi-rate sampling sensor and control
Evaluation:
The complex of system is in proportion to the dimensions of the state
and the input. The computation overhead increases with the dimensions.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

16. Methodology Two: Control Part
Queuing Method
Luck and Ray,1990;1994 deterministic delay compensation
Chan and Ozguner, 1995 probabilistic delay compensation
Evaluation:
The dynamic model of the plant is required to be very precise.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

17. Methodology Two: Control Part
Perturbation method
Walsh et al.,1999a 1999b；2001 formulated the network delay effects in an NCS as the vanishing perturbation of a continuous-time system
Branicky et al.,2000 , Zhang et al.,2001 use this method to compute upper value of MATI , which is far less than value obtained by simulation.
(This method is conservative)
Evaluation:
- The dynamic model of the plant is not necessary to be very precise, may be non-linear
- There is no network link between controller and actuator.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

18. Methodology Two: Control Part
LQG/H2
Nilsson 1998 proposed the optimal stochastic control method to control an NCS on random delay networks. The optimal stochastic control method treats the effects of the random network delays in an NCS as a Linear –Quadratic-Gaussian (LQG) problem. Markovian delay case was also analyzed .
Krtolica,1994 ，Montestruque,2002
Evaluation:
- Better than the determinative method at dynamic performance
-Storage overhead of past information.
-Time delay less than one sampling period.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

19. Methodology Three: Control & Scheduling
Seto et al consider optimal sampling period selection for a set of digital controllers. The performance of each controller is described by a cost function (a performance index), which is approximated by an exponential function of the sampling frequency. An optimization problem is formulated, where the sum of the cost functions should be minimized subject to the schedulability constraint. Both fixed priority and earliest-deadline-first scheduling is considered.
Evaluation:
- Enhance the processor’s task schedulability by allowing the task frequencies
to change in the context of real-time control system performance
-Improve the overall system performance
- do not consider the input-output latency in the controllers
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

20. Methodology Three: Control & Scheduling
Ryu and Hong 1997, 1998 proposed the sampling period optimization problem under the schedulability constraints.
Main contribution: a systematic method to derive task-level timing constraints from system-level timing constraints establishing temporal relationship between the system’s external input and outputs
maximum loop processing period,
maximum allowable input-output latency
period ,deadlines
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

21. Methodology Three: Control & Scheduling
Zhang formulated the optimal scheduling problem under both RM-schedulability constaints and NCS stability constraints.
Anton Cervin 2003, two Matlab-based toolboxes Jitterbug , TrueTime.
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ZJU-NLICT-NCS Research Group By Shanbin Li

22. ZJU-NLICT-NCS Research Group By Shanbin Li
Our Results
1, Li Shanbin, Wang Zhi, Zhang Weidong, Sun Youxian, Research status and prospect of networked control systems (In Chinese), Journal of Information and Control, 2003.
2, Li Shanbin, Ren Xudong, Wang Zhi, Sun Youxian, Real-time analysis of CAN for networked control systems (In Chinese), Journal of chemical engineering automation and instrument, 2003
3,Li Shanbin,Wang Zhi, Sun Youxian, Fundamental Problems of Networked Control System from the view of Control and Scheduling, IEEE IECON'02, Spain，2002
4. Li Shanbin,Wang Zhi, Sun Youxian , A Novel Auto-tuning Robust PID Controller for Networked Control System, IEEE IECON'03, USA, 2003
5. Li Shanbin,Wang Zhi, Sun Youxian, Auto-tuning Robust Digital PID Controller for Networked Control System, Journal of Zhejiang Universtiy (Engineering), Accepted
6. Li Shanbin, Wang Zhi, Sun Youxian, Guaranteed cost control and its application to networked control systems, IEEE ISIE’04, France, 2004
7. Li Shanbin, Wang Zhi, Sun Youxian, Delay-Dependent Controller Design for Networked Control Systems with Long Time Delays :An Iterative LMI Method, IEEE WCICA, China, 2004
8. Xudong Ren, Shanbin Li, Zhi Wang, Mingze Yuan and Youxian Sun, “A QoS management scheme for paralleled Networked Control Systems,” IECON’03, USA, 2003
9. Xudong Ren , Shanbin Li ,Zhi Wang , Youxian Sun, A QoS management scheme for paralleled Networked Control Systems, Journal of Zhejiang University, Accepted.
10. Ren Xudong ,The Research on Real-time Scheduling Algorithms and its Applications to Paralleled Networked Control Systems, Master Thesis of Zhejiang Universtiy
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

23. Current focus: packet losses
Two reason for packet losses
The network is unreliable
The measurement is purposely dropped to stay within an allocated transmission rate, namely congestion control
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

24. ZJU-NLICT-NCS Research Group By Shanbin Li
Packet losses model
(m,k)
Markov Chain
Hidden Markov Chain
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ZJU-NLICT-NCS Research Group By Shanbin Li

25. ZJU-NLICT-NCS Research Group By Shanbin Li
Packet losses model
(25-1)
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ZJU-NLICT-NCS Research Group By Shanbin Li

26. ZJU-NLICT-NCS Research Group By Shanbin Li
Packet losses model
Independent losses
Gilbert-Elliot losses
Fixed-length burst losses
(26-1)
(26-2)
(26-3)
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ZJU-NLICT-NCS Research Group By Shanbin Li

27. NCS model with packet losses (1)
(27-1)
(27-2)
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ZJU-NLICT-NCS Research Group By Shanbin Li

28. NCS model with packet losses (1)
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

29. NCS model with packet losses (1)
(29-1)
The details refer to Babak Azimi-Sadjadi "Stability of networked control systems in the presence of packet losses", IEEE CDC'03
Limitation: the model doesn’t take the delay into account
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ZJU-NLICT-NCS Research Group By Shanbin Li

30. NCS model with packet losses (2)
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ZJU-NLICT-NCS Research Group By Shanbin Li

31. NCS model with packet losses (2)
(31-1)
(31-2)
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ZJU-NLICT-NCS Research Group By Shanbin Li

32. NCS model with packet losses (2)
(32-1)
(32-2)
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

33. NCS model with packet losses (2)
(33-1)
(33-2)
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

34. NCS model with packet losses (2)
(34-1)
The details refer to Hai Lin, Guisheng Zhai, Panos J.Antsaklis, Robust stability and disturbance attenuation analysis of a class of networked control systems, IEEE CDC’03
Limitation: Delay shorter than one sampling time.
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

35. Analysis fundament for NCS with packet losses
Markov Jump Linear System Theory
Dynamic Programming
Stochastic System Theory, including estimation and filtering
Soft Real-time Scheduling Theory
Donglin Liu et al. Firm real-time system scheduling based on a novel QoS constraint, IEEE RTSS’03
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

36. My NCS model with packet losses
Long time delay+ Hidden makovian packet losses
Ongoing………
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

37. ZJU-NLICT-NCS Research Group By Shanbin Li
Future work
Scheduling method for NCS in the presence of packet losses
Congestion control
The relationship between the parameters of network QoS and those of system QoP
Stability analysis and controller design of NCS in the presence of packet losses
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

38. ZJU-NLICT-NCS Research Group By Shanbin Li
Summary
There is a challenge for better solution methods for the multidisciplinary systems combining control, communication, computation and other disciplines.
Research groups:
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li

39. ZJU-NLICT-NCS Research Group By Shanbin Li
Questions and remarks?
MSN:
2018/11/27
ZJU-NLICT-NCS Research Group By Shanbin Li