Control Synthesis for a Class of Hybrid Systems Subject to Configuration-Based Safety Constraints

We examine a class of hybrid systems which we call Composite Hybrid Machines (CHM's) that consists of the concurrent (and partially synchronized) operation of Elementary Hybrid Machines (EHM's). Legal behavior, specified by a set of illegal configurations that the CHM may not enter, is to be achieved by the concurrent operation of the CHM with a suitably designed legal controller. In the present paper we focus on the problem of synthesizing a legal controller, whenever such a controller exists. More specifically, we address the problem of synthesizing the minimally restrictive legal controller. A controller is minimally restrictive if, when composed to operate concurrently with another legal controller, it will never interfere with the operation of the other controller and, therefore, can be composed to operate concurrently with any other controller that may be designed to achieve liveness specifications or optimality requirements without the need to reinvestigate or reverify legality of the composite controller. We confine our attention to a special class of CHM's where system dynamics is rate-limited and legal guards are conjunctions or disjunctions of atomic formulas in the dynamic variables (of the type x less than or equal to x(sub 0), or x greater than or equal to x(sub 0)). We present an algorithm for synthesis of the minimally restrictive legal controller. We demonstrate our approach by synthesizing a minimally restrictive controller for a steam boiler (the verification of which recently received a great deal of attention)

Modeling and Control of Discrete Event Systems Using Finite State Machines with Variables and Their Applications in Power Grids

Control theories for discrete event systems modeled as finite state machines have been well developed to address various fundamental control issues. However, finite state machine model has long suffered from the problem of state explosion that renders it unsuitable for some practical applications. In an attempt to mitigate the state explosion problem, we propose an efficient representation that appends finite sets of variables to finite state machines in modeling discrete event systems. We also present the control synthesis techniques for such finite state machines with variables (FSMwV). We first present our notion and means of control under this representation. We next present our algorithms for both offline and online synthesis of safety control policies. We then apply these results to the control of electric power grids

Management Of Plug-In Electric Vehicles And Renewable Energy Sources In Active Distribution Networks

Near 160 million customers in the U.S.A. are served via distribution networks (DNs). The increasing penetration level of renewable energy sources (RES) and plug-in electric vehicles (PEVs), the implementation of smart distribution technologies such as advanced metering/monitoring infrastructure, and the adoption of smart appliances, have changed distribution networks from passive to active. The next-generation of DNs should be efficient and optimized system-wide, highly reliable and robust, and capable of effectively managing highly-penetrated PEVs, RES and other controllable loads. To meet new challenges, the next-generation DNs need active distribution management (ADM). In this thesis, we study the management of PEVs and RES in active DNs. First, we propose a novel discrete-event modeling method to model PEVs and other loads in distribution networks. In addition, a new optimization algorithm to integrate as many PEVs as possible in DNs without causing voltage issues, including the violation of voltage security ranges and voltage stability, is studied. To further explore the active management of PEVs in the DNs, we develop a universal demonstration platform, consisting of software packages and hardware remote terminal units. The demonstration platform is designed with the capabilities of measurement, monitoring, control, automation, and communications. Furthermore, we have studied the reactive power management in microgrids, a special platform to integrate distributed generations and energy storage in DNs. To solve possible voltage security issues in a microgrid with high penetration of single-phase induction machines under the condition of fault-induced islanding, a voltage-sensitivity-based reactive power management algorithm is proposed

Supervisory control of discrete-event systems with output : application to hybrid systems

In this thesis, the problem of supervisory control of Discrete-Event Systems (DES) with output is presented and discussed at length. In such systems, causal output functions are employed to assign each sequence of inputs with a corresponding sequence of outputs. When the specification of the desired behavior is given by a formal language over the output alphabet, necessary and sufficient conditions are derived for the existence of nonblocking input as well as nonblocking output supervisory controls. An algorithm is presented to extend the results of nonblocking input/output supervisory control from language-based framework into finite automata framework, making the proposed results applicable to large scale discrete-event systems. The idea of siblings is introduced to solve the problem of nondeterminism in discrete-event abstractions of hybrid systems, giving rise to the development of a theory for nonblocking supervisory control of hybrid systems. Our results enable one to apply classical supervisory control theory to design supervisors for DES approximations of hybrid systems, and to import many interesting concepts from classical theory such as modular and hierarchical control

Extension and Implementation of Look-ahead Supervisory Control with Buffering

The Supervisory Control Theory of Discrete Event Systems (DES) provides procedures 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 onboard 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 systems, an approach is proposed in the literature where at any given time, supervisory commands 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 compute control commands. To mitigate this problem, an approach has been proposed called 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 designed 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 information 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 requirement and computational power