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Conclusion, Future Scope and Challenges

  • Dipesh H. ShahEmail author
  • Axaykumar Mehta
Chapter
  • 593 Downloads
Part of the Studies in Systems, Decision and Control book series (SSDC, volume 132)

Abstract

In this book, a novel method of designing discrete-time sliding mode controller in the presence of fractional delay along with packet loss occurrence due to network medium is presented. Firstly, the effect of deterministic type fractional delay is compensated using Thiran’s approximation technique and the compensated state information is used for the design of sliding surface. A switching type discrete-time networked sliding mode controller is designed using the compensated sliding surface which computes the control sequences in the presence of matched uncertainty. The condition for stability of the closed-loop system is derived using Lyapunov approach.

8.1 Conclusion and Future Scope

In this book, a novel method of designing discrete-time sliding mode controller in the presence of fractional delay along with packet loss occurrence due to network medium is presented. Firstly, the effect of deterministic type fractional delay is compensated using Thiran’s approximation technique and the compensated state information is used for the design of sliding surface. A switching type discrete-time networked sliding mode controller is designed using the compensated sliding surface which computes the control sequences in the presence of matched uncertainty. The condition for stability of the closed-loop system is derived using Lyapunov approach. The efficacy of the proposed algorithms is tested on DC servo motor setup with different network delays and external disturbances. The results are compared with the conventional SMC, and it is observed that the DSMC design using Thiran’s approximation compensates the fractional delays satisfactorily. The major drawback of switching type DSMC is that it induces unmodeled dynamics and the large QSMC band which compromise the robustness property. To overcome this issue, a non-switching type discrete-time sliding mode controller with Thiran’s approximation technique is proposed. The efficacy of the proposed algorithm is tested through illustrative example as well as DC servo motor setup with different deterministic fractional delays and matched uncertainty. The results are also compared with switching type SMC as well as conventional SMC without delay compensation. It is observed that the proposed non-switching type DSMC algorithm not only rapidly converges but also reduces the amplitude of control signal and offers better fractional delay compensation. The efficacy of the proposed control algorithm is also tested under real-time networks like CAN and Switched Ethernet as a network medium in the presence of packet loss condition. From the simulation and experimental results, it is observed that the proposed DSMC law using Thiran’s approximation compensates the effect of fractional network delay even in the presence of real-time networks and packet loss situation. The DSMC algorithms are further extended for output feedback control using the well-known multirate output feedback approach.

The DSMC control law is further extended for random fractional delays with single packet loss situation. The random fractional delay is modeled using Poisson’s distribution function, and packet loss is modeled using probability distribution function. The stability condition derived for the closed-loop system ensures finite-time convergence in the presence of random fractional delay, packet loss and matched uncertainty. The effectiveness of the proposed control algorithm is examined through DC servo motor setup under random fractional delay and single packet loss. The results show that the DSMC control law derived using Thiran’s approximation compensates random fractional delay accurately even in the presence of single packet loss with probability of \(30\%\) as well as networked delays having values greater than sampling interval.

Lastly, the DSMC algorithm is extended for random fractional delay with multiple packet loss situations. The multiple packet loss situation is modeled using probability distribution function, while random fractional delay is modeled using Poisson’s distribution. The proposed DSMC control law effectively compensates the random fractional delay with multiple packet loss. The stability of the closed-loop NCS is assured through Lyapunov approach under multiple packet transmission. The efficacy of proposed DSMC algorithm is verified through DC servo motor plant under random fractional delay, multiple packet loss and matched uncertainty. The results show that the proposed control law compensates the effect of random fractional delay even in the presence of multiple packet loss with probability of \(30\%\) as well as networked delays greater than sampling interval.

In future, the DSMC algorithm can be extended for Wireless Networked Control System (WNCS). Also, the efficacy of the proposed algorithm needs to be checked for direct structure NCS, hierarchical structure and shared network structure NCS.

8.2 Challenges

In Networked Control System although much work has been done in last two decades. However, still there are various challenges that need to be solved while designing the control algorithm such as
  • There are no standard algorithm available in the literatures that discusses the variable packet loss model. The main disadvantages in existing models are random time delay and packet loss lumped together. So it is difficult to differentiate the effect of losses in the system response. Thus, there is need for developing some model that takes care of only packet loss.

  • In NCS, packet disorder is also one of the challenging issues that occurs in event-triggered model. In the literature, it is assumed that packet disorder does not take place in such type of models. However, in real-time applications this assumption does not hold true. So, there is a need of control algorithm that discusses the packet disorder in event-triggered model.

  • The concept of distributed networked control is still an attractive and challenging area for the researchers in Networked Control System. In distributed networked control, large number of sensors and actuators are connected to the various controllers through different topologies which causes random time delay and packet loss at each level depending on the type of topology and communication medium. These factors make the analysis and synthesis more complicated and challenging for distributed networked control systems.

  • There is also need to study the reliability issues for the Networked Control System.

  • Investigations related to packet dropout and network-induced delays in industrial-based NCS are popular. However, studies related to the possible positive effects of these parameters are still not conducted. Designing of the controller which emphasizes these effects is interesting.

  • Apart from random time delay and packet loss issues, there are various concerns such as bandwidth sharing, security and resource allocation in NCS that need to be studied for better performance of Networked Control System.

Copyright information

© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  1. 1.Department of Instrumentation and ControlSardar Vallabhbhai Patel Institute of TechnologyAnandIndia
  2. 2.Department of Electrical EngineeringInstitute of Infrastructure Technology Research and ManagementAhmedabadIndia

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