Global Petri net modeling of hybrid systems and fault analysis
Creators: name: Riz̤āʼī, Muḥammad
Publisher: name: University of British Columbia
Year: 2009

description: In this dissertation, a new methodology for the modeling and analysis of hybrid systems is presented. Hybrid systems are those which have both event-driven (asynchronous) and time-driven (synchronous) elements. This new methodology is based on an extension of the Petri net (PN) theory. Petri nets have proven themselves to be an excellent modeling tool for discrete-event systems and computer architectures. This new extension of Petri nets, which is called a Global Petri Net (GPN), provides a means for extending these capabilities to discrete-time systems. Although, many extensions of PNs have been developed over the years, the GPN methodology is the first one to perform the modeling, analysis, and simulation of discrete-event and discrete-time dynamic systems in a unified PN framework. The GPN is formally defined, and the structural and behavioral differences between PNs and GPNs are presented. The derivation of GPNs from the basic PN, and derivation of the GPN dynamic equations are also given. Next, two modeling examples are provided. These two examples show that the GPN formalism can be used to model hybrid systems in various application areas. Analysis techniques, which can be used to investigate the system properties, are developed. These analysis techniques are based on the construction of the system reachability tree and linear algebraic equations. The properties which are analyzed by these techniques include controllability, boundedness, stability, and conservation. Theorems and proofs of these properties are stated and proven. An example of a distributed hybrid system is modeled at various levels of abstraction. This system consists of a hydraulic control system and its interfaces with a bus-based communication system. At the highest level, the system is modeled as a discrete-event system. At the lowest level, where the details of the hydraulic control system are modeled, a hybrid model is used. The nets at all levels are simulated and analyzed by the global Petri net simulation and analysis tool (GPNSAT), written specifically for this research. Various system level faults for a hydraulic control system are modeled and simulated. For each fault type, the simulation shows how various system outputs are affected. At each level of abstraction, the hybrid system is simulated and analyzed for various properties, such as stability, boundedness, controllability, conservativeness, and liveness. Analysis methods developed for GPNs provide distinct fault signatures for each of the system fault types. These fault signatures can be used to distinguish successfully each fault in a detection and recognition scheme. The major contribution of this thesis is the extension of Petri nets to encompass hybrid systems. This new modeling approach can be applied to a variety of systems in application areas such as, manufacturing, multimedia, production, digital, and communication systems. This extension also enables one to examine the impact of faults in either part of the system (synchronous or asynchronous) and the effect that fault would have on the other parts of the system. These effects can be analyzed or simulated either at design time or run-time.