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This dissertation studies the model reduction and distributed control problems for interconnected systems, i.e., systems that consist of multiple interacting agents/subsystems. The study of the analysis and synthesis problems for interconnected systems is motivated by the multiple applications that can benefit from the design and implementation of distributed controllers. These applications include automated highway systems and formation flight of unmanned aircraft systems. The systems of interest are modeled using arbitrary directed graphs, where the subsystems correspond to the nodes, and the interconnections between the subsystems are described using the directed edges. In addition to the states of the subsystems, the adopted frameworks also model the interconnections between the subsystems as spatial states. Each agent/subsystem is assumed to have its own actuating and sensing capabilities. These capabilities are leveraged in order to design a controller subsystem for each plant subsystem. In the distributed control paradigm, the controller subsystems interact over the same interconnection structure as the plant subsystems. The models assumed for the subsystems are linear time-varying or linear parameter-varying. Linear time-varying models are useful for describing nonlinear equations that are linearized about prespecified trajectories, and linear parameter-varying models allow for capturing the nonlinearities of the agents, while still being amenable to control using linear techniques. It is clear from the above description that the size of the model for an interconnected system increases with the number of subsystems and the complexity of the interconnection structure. This motivates the development of model reduction techniques to rigorously reduce the size of the given model. In particular, this dissertation presents structure-preserving techniques for model reduction, i.e., techniques that guarantee that the interpretation of each state is retained in the reduced order system. Namely, the sought reduced order system is an interconnected system formed by reduced order subsystems that are interconnected over the same interconnection structure as that of the full order system. Model reduction is important for reducing the computational complexity of the system analysis and control synthesis problems. In this dissertation, interior point methods are extensively used for solving the semidefinite programming problems that arise in analysis and synthesis. / Ph. D. / The work in this dissertation is motivated by the numerous applications in which multiple agents interact and cooperate to perform a coordinated task. Examples of such applications include automated highway systems and formation flight of unmanned aircraft systems. For instance, one can think of the hazardous conditions created by a fire in a building and the benefits of using multiple interacting multirotors to deal with this emergency situation and reduce the risks on humans. This dissertation develops mathematical tools for studying and dealing with these complex systems. Namely, it is shown how controllers can be designed to ensure that such systems perform in the desired way, and how the models that describe the systems of interest can be systematically simplified to facilitate performing the tasks of mathematical analysis and control design.

Direct Load Control (DLC) -- the direct control of customer loads by an electric utility for the economic and reliable operation of the power system, is an important and active element of Load Management (LM). Currently attention has focussed on the integration of DLC into system operations. However, as yet, DLC is regarded as a discretionary resource to be used by the system operator based on informed judgment. The integration process has therefore, concentrated on improving the informational inputs to the operator. This dissertation extends the integration from that of a discretionary resource to a dispatchable system resource. The concept of the dynamic dispatch of DLC is formulated and defined to be an online evaluation and utilization of DLC for optimum benefit to the utility, as system conditions change. The concept envisages the use of DLC in an automated mode and coordinated with other system resources for optimum benefit. An important and integral part of the research effort is the development of a cost characterization of DLC. A closed form solution, using a dynamic programming framework, has been developed to estimate the costs of DLC dispatch. The derivation takes into account all operational constraints on the utilization of DLC -- payback characteristics, maximum on-times and minimum recovery times. The cost, defined as the difference in the fuel costs with and without DLC dispatch, were found to be dependent on the cost characteristics of the online generators and the load shape impacts of DLC dispatch. The dynamic dispatch concept is concretized by a power system operations model which incorporates DLC dispatch for fuel cost minimization and peak load shaving. The two modes are toggled by the dispatch algorithm as system conditions change. Results from the model are presented for several combinations of system conditions and DLC system parameters. / Ph. D.

As necessity for improvement in system operation demands the implementation of distribution automation, design of the protection system becomes more involved. Several goals of distribution automation -- improved customer reliability, reduced systems losses, and balancing of substation loading -- are dependent on the ability to perform automatic circuit reconfigurations. A prerequisite for implementing automatic circuit reconfiguration is that the protection system design must operate properly for all configurations. An integrated expert system for the protection system design of interconnected distribution circuits has been developed using the DANE engineering workstation. The expert system incorporates the basic requirements and guidelines as specified by IEEE for protection system design. The expert system uses a relational database management system, integrates system data, and provides a graphical user interface. The expert system incorporates both procedural and declarative, or query, operating modes. Rules dealing with the coordination, placement and selection of protective devices are presented that are used to dynamically, incorporate expert knowledge into the knowledge base. The protection system designer controls which rules are implemented in the design. An example protection system design is presented using the integrated expert system developed for DANE. The example problem consists of three interconnected distribution circuits. Dynamic knowledge, created by the expert system from the rules and system data, is used in the design. System data is presented pertaining to the circuits along with the created dynamic knowledge. The implemented rules dealing with the coordination, placement and selection of protective devices are presented, along with all associated parameter values. The final protection system design and results are presented in a research report. / Ph. D.

A novel probabilistic method has been developed for modelling the operation of energy storage in electricity systems with significant amounts of wind and solar powered generation. This method is based on a spectral analysis of the variations of wind speed and solar irradiance together with profiles of electrical demand. The method has been embodied in two Matlab computer programs: Wind power only: This program models wind power on any time scale from seconds to years, with limited modelling of demand profiles. This program is only capable of modelling stand-alone systems, or systems in which the electrical demand is replaced by a weak grid connection with limited export capacity. 24-hours: This program models wind power, solar PV power and electrical demand, including seasonal and diurnal effects of each. However, this program only models store cycle times (variations within a time scale) of 24 hours. This program is capable of modelling local electrical demand at the same time as a grid connection with import or export capacity and a backup generator. Each of these programs has been validated by comparing its results with those from a time step program, making four Matlab programs in total. All four programs calculate the power flows to and from the store, satisfied demand, unsatisfied demand and curtailed power. The programs also predict the fractions of time that the store spends full, empty, filling or emptying. The results obtained are promising. Probabilistic program results agree well with time step results over a wide range of input data and time scales. The probabilistic method needs further refinement, but can be used to perform initial modelling and feasibility studies for renewable energy systems. The probabilistic method has the advantage that the required input data is less, and the computer run time is reduced, compared to the time step method.

The exploitation of lignocellulosic materials with the aim of producing high value-added products will potentially counteract concerns related to the depletion of fossil resources or exponential population growth. Bioethanol produced from lignocellulosic agriculture residue exhibits promising alternative to the petroleum-based fossil fuel which reduces net emission of greenhouse gases (GHG). But, due to certain technological barriers, the large scale production of lignocellulosic bioethanol has not been successfully commercialized. In this thesis, membrane filtration as an energy efficient separation process with low environmental impact was chosen with a possibility of improvement. Interconnected multi-staged microfiltration submerged membrane bioreactors (MBRs) set-up has been applied in order to separate suspended solids, obtain high concentration of yeast inside the bioreactor, and recover particle-free ethanol stream in a continuous high productivity process. The MBRs were effectively optimized comparing to different constant permeate fluxes of 21.9 LMH, 36.4 LMH, and 51 LMH. Moreover, membrane bioreactor performed effectively at low flux 21.9 LMH up to 262 h comparing to other applied fluxes. During continuous hydrolysis, membrane showed the capability of lignin recovery nearly 70% of medium SS content in all applied flux. Although the conversion rate of total sugars by concentrated cells were similar, yeast cells proved the capability of inhibitor tolerance, and to co-utilize 100% of glucose and up to 89% of xylose, resulted in bioethanol volumetric productivity of 0.78 g ethanol/l per hour 1.3 g ethanol/l per hour and 1.8 g ethanol/l per hour for 21.9 LMH, 36.4 LMH, and 51 LMH respectively. Moreover, the effect of different factors such as filtration flux, medium quality and backwashing on fouling and cake-layer formation in submerged MBRs during continuous filtration was thoroughly studied.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 328-332. / by Marcel Coderch i Collell. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Sherman Man Chan. / Ph.D.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

This research addresses some of the difficulties faced when operating voltage controlled inverters with synchronous generators in microgrids. First, an overview of microgrid value propositions is provided, and the problems faced when attempting to use microgrids to provide improved power quality are discussed. Design considerations for different types of microgrids are provided to enable microgrids to deliver the desired functionality without adding unnecessary cost. The main body of this research investigates the poor transient load sharing encountered between voltage controlled inverters and synchronous generators in islanded operation. Poor transient load sharing results in high peak inverter rating requirements and high cost. The tradeoff between power quality and power sharing is highlighted, and methods to improve transient load sharing are proposed. The use of current limiting to protect inverters during faults and overloads is also investigated. Stability problems are identified when using simple inverter current limiting methods when operating in parallel with synchronous generators. Virtual impedance current limiting is proposed to improve transient stability during current limiting. The methods proposed in this thesis for mitigating inverter overloads and faults will allow for more reliable and cost effective application of inverter based distributed energy resources with synchronous generators in microgrids.