Extension and Implementation of Look-ahead Supervisory Control with Buffering Faiz Ur Rehman A Thesis in The Department of Electrical and Computer Engineering Presented in Partial Fulfillment of the Requirements for the Degree of Master of Applied Science (Electrical and Computer Engineering) at Concordia University Montreal,´ Quebec,´ Canada August 2020 c Faiz Ur Rehman, 2020 CONCORDIA UNIVERSITY School of Graduate Studies This is to certify that the thesis prepared By: Faiz Ur Rehman Entitled: Extension and Implementation of Look-ahead Supervisory Con- trol with Buffering and submitted in partial fulfillment of the requirements for the degree of Master of Applied Science (Electrical and Computer Engineering) complies with the regulations of this University and meets the accepted standards with re- spect to originality and quality. Signed by the Final Examining Committee: Chair Dr. K. Skonieczny External Examiner Dr. W.F. Xie (MIAE) Examiner Dr. K. Skonieczny Supervisor Dr. S. Hashtrudi Zad Approved by Yousef Shayan, Chair Department of Electrical and Computer Engineering 2020 Dr. Mourad Debbabi, Dean Faculty of Engineering and Computer Science Abstract Extension and Implementation of Look-ahead Supervisory Control with Buffering Faiz Ur Rehman The Supervisory Control Theory of Discrete Event Systems (DES) provides proce- dures to design supervisors to control plants modeled as DES. The computed supervisor issues control commands to ensure design specifications, such as safety constraints, are met. In the supervisor design process, the plant and design specification models are used to obtain the supervisor in the form of a DES. In this approach, the control commands are effectively pre-calculated before implementation; thus the approach is known as Offline Supervisor Design. The challenge associated with this method is that it requires large on- board memory for supervisor (due to typically large DES models involved). Such large memory is not available on embedded systems. In order to make the implementation of supervisory control feasible for embedded sys- tems, an approach is proposed in the literature where at any given time, supervisory com- mands are computed on-the-fly based on models for plant and specifications covering a small window into the future (i.e., lookahead window). This method needs a significantly smaller onboard memory. As a result, however, frequent control command computation is needed. This could pose a implementation challenge since control commands must be computed after every new event in the plant. Sometimes two (or more) consecutive events could occur in rapid succession in the plant and there may not be enough time to com- pute control commands. To mitigate this problem, an approach has been proposed called iii Lookahead Supervision with Buffering in which commands are computed and buffered in advance for a window. This thesis makes contributions to the underlying theory of lookahead policy with buffering. Specifically it proposes a method to use the timed model of the plant to compute the timing information of event sequences. This timing information is used in choosing the buffer size and was previously obtained experimentally. The thesis also develops a method for computing plant and specification models over the loakahead window that is suited for computer coding. The thesis also implements the lookahead supervision with command buffering. To study the feasibility of implementation and the complexity of proposed controller in detail, a two-degree-of-freedom solar tracker equipped is used as plant. The goal is to generate supervisory commands for maneuvering the solar tracker to find a bright light source for charging battery. For implementation, all supervisory control algorithms are written in C language for faster computation time. Look-ahead policy with command buffering is de- signed and implemented. In several tests, the supervisor successfully calculates on-line the control commands in a timely fashion and maneuvers the solar tracker to the bright source while respecting design specifications. The experimental results show that the timing infor- mation calculated with the proposed method based on timed model match the actual plant behavior. Furthermore, the experiments demonstrate that the length of command buffer (as design parameter) can be used to achieve a compromise between onboard memory require- ment and computational power. iv Acknowledgments In the name of ALLAH Almighty, the Most Merciful and the Most Beneficent. All praises and thanks be to Him. First, I would like to express my sincere gratitude to my supervisor Dr. Shahin Hashtrudi Zad, for his invaluable guidance throughout my research. This work would not have been possible without his continuous support. Second, I would like to thank my loving parents, sisters, and brother for their love, prayers, support, and encouragement. I especially dedicate this thesis to my father, who has always been an inspiration to me. Third, I would like to thank the Embedded team and the management of Neptronic for their support and flexibility that helped me throughout my work. Especially, my co-orkers who kept me motivated. Finally, I would like to thank my friends, who were always there to encourage me. v Contents List of Figures ix List of Tables xii 1 Introduction1 1.1 Supervisory Control Theory for DES.....................2 1.2 Literature Review...............................4 1.2.1 Autonomous Systems and Space Applications............4 1.2.2 Supervisory Control Theory.....................6 1.2.3 Timed Discrete Event Systems.................... 10 1.3 Thesis Objectives and Contributions..................... 11 1.4 Thesis Outline................................. 12 2 Background 13 2.1 Discrete Event System............................ 13 2.1.1 Languages and Preliminaries..................... 14 2.1.2 Automata and Operations...................... 15 2.2 Timed Discrete Event Systems (TDES)................... 19 2.3 Supervisory Control Theory......................... 27 3 Research Objectives 38 vi 3.1 Review of Limited Look-ahead Policy with Buffering............ 39 3.1.1 Minimum Look-ahead Window Size................. 39 3.1.2 Supervisor Validity of LLP with Buffering............. 40 3.1.3 Choosing Buffer Size......................... 43 3.2 Thesis Objectives............................... 45 4 Development of Discrete Event Control Kit for Embedded Systems 47 4.1 Structures and Data Types for DECK Procedure............... 48 4.2 DECK Procedures............................... 51 4.3 Automaton I/O Functions........................... 60 4.4 Time Complexity Comparison........................ 64 5 Experimental Setup and Supervisory Design Setup 68 5.1 System Hardware............................... 69 5.1.1 Remote Station............................ 69 5.1.2 Ground Station............................ 73 5.2 Untimed DES Model and Supervisor Design................. 74 5.2.1 Components............................. 74 5.2.2 Interactions.............................. 84 5.2.3 Specifications............................. 86 5.2.4 Supervisor Synthesis......................... 89 6 Calculation of Sequence Duration using Timed DES 91 6.1 Modeling of Solar Tracker as Timed DES.................. 91 6.1.1 Modeling Time Bounds of Events.................. 92 6.1.2 Selection of Tick Size........................ 96 6.1.3 TDES Model of Plant Under Supervision.............. 100 6.2 Analysis of TDES under Supervision..................... 103 vii 7 Control Implementation and Analysis 108 7.1 Communication Link............................. 110 7.2 Execution of Controller............................ 112 7.2.1 Regular LLP............................. 117 7.2.2 LLP with Buffering.......................... 118 7.2.3 Computation Time Analysis of LLP................. 120 7.2.4 Computation Time per Event..................... 123 7.2.5 Selection of Buffer Size for LLP................... 125 8 Conclusion 128 8.1 Summary................................... 128 8.2 Future Work.................................. 129 Appendix A TTCT File Templates 131 Appendix B Full Sweep Spec Model 133 Appendix C Communication Packets 134 Bibliography 140 viii List of Figures Figure 1.1 Small Factory.............................2 Figure 1.2 DES model of Small Factory......................3 Figure 1.3 Plant under supervision (closed-loop system).............4 Figure 1.4 Real-time Control Architecture [1]..................7 Figure 2.1 Automaton G............................. 16 Figure 2.2 Gact .................................. 25 Figure 2.3 TTG of Gact .............................. 26 Figure 2.4 Closed Loop plant........................... 28 Figure 2.5 Block diagram of LLP supervisor................... 31 Figure 3.1 LLP with expanded window...................... 40 Figure 3.2 Sub-expanded Tree.......................... 42 Figure 3.3 Timeline of LLP with buffering................... 44 Figure 4.1 BFS Example............................. 52 Figure 4.2 Self-looped Automaton G....................... 58 Figure (a) G................................ 58 Figure (b) Gs................................ 58 Figure 4.3 Sync Procedure............................ 59 Figure (a) G................................ 59 Figure (b) H................................ 59 Figure (c) sync of G,H........................... 59 ix Figure 4.4 Graphical representation of automatons................ 61 Figure (a) Automaton with name..................... 61 Figure (b) Automaton with code...................... 61 Figure 5.1 Solar tracker