Energy efficiency and renewable energy become more attractive in smart grid. In order to efficiently reduce global energy usage in building energy systems and to improve local environmental sustainability, it is essential to optimize the operation and the performance of combined heat and power (CHP) systems. In addition, intermittent renewable energy and imprecisely predicted customer loads have introduced great challenges in energy-efficient buildings' optimal operation. In the deterministic optimal operation, we study the modeling of components in energy-efficient building systems, including the power grid interface, CHP and boiler units, energy storage devices, and building appliances. The mixed energy resources are applied to collaboratively supply both electric and thermal loads. The results show that CHP can effectively improve overall energy efficiency by coordinating electric and thermal power supplies. Through the coordinated operation of all power sources, the daily operation cost of building energy system for generating energy can be significantly reduced. In order to address the risk from energy consumption forecast errors and renewable energy production volatility, we utilize the approach of stochastic programming and robust optimizations to operate energy-efficient building systems under uncertainty. The multi-stage stochastic programming model is introduced so that the reliable operation of building energy systems would be probabilistically guaranteed with stochastic decisions. The simulation results show that the stochastic operation of building energy systems is a promising strategy to account for the impact of the uncertainty on power dispatch decisions of energy-efficient building systems. In order to provide absolute guarantee for the reliable operation of building energy systems, a robust energy supply to electric and thermal loads is studied by exploring the effectiveness of energy storage on energy supply against the uncertainty. The robustness can be adjusted to control the conservativeness of the proposed robust operation model. For the purpose of achieving adaptability in the robust optimal operation and attaining robustness in the stochastic optimal operation of building energy systems, we also develop an innovative robust stochastic optimization (RSO) model. The proposed RSO model not only overcomes the conservativeness in the robust operation model, but also circumvents the curse of dimensionality in the stochastic operation model.

Voltage stability studies (VSS) of the electric network is a crucial factor to make the system operate in stable region and to prevent power blackouts. There are several commercial tools available for VSS of electric transmission systems (TS) but not many for distribution systems (DS). With increasing penetration of distributed renewable generations and meshed network within DS, shipboard power system (SPS) and microgrid, these VSS tools need to be extended for DS. Due to inherent characteristic like high R/X ratio, three phase and unbalanced operation, DS or SPS requires different mathematical approach than TS. Unbalanced three phase power flow and continuation power flow tools were developed using current injection and corrector predictor methods in this work for VSS. Maximum loading point for given DS or SPS can be computed using developed tools to guide required preventive and corrective actions. Developed tool was tested and validated for several different test cases.

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This research focuses on developing novel approaches in load balancing and restoration problems in electrical power distribution systems. The first approach introduces an inter-connected network topology, referred to as (n, k)-star topology. While power distribution systems can be constructed in different communication network topologies, the performance and fault assessment of the networked systems can be challenging to analyze. The (n, k)-star topologies have well defined performance and stability analysis metrics. Typically, these metrics are defined based on: i) degree, ii) diameter, and iii) conditional diagnosability of a faulty node. These parameters could be evaluated and assessed before a physical (n, k)-star topology power distribution system is constructed. Moreover, in the second approach, we evaluate load balancing problems by using a decentralized algorithm, i.e., the Multi-Agent System (MAS) based consensus algorithm on an (n, k)-star power topology. With aforementioned research approaches, an (n, k)-star power distribution system can be assessed with proposed metrics and assessed with encouraging results compared to other topology networked systems. Other encouraging results are found in efficiency and performance enhancement during information exchange using the decentralized algorithm. It has been proven that a load balance solution is convergent and asymptotically stable with a simple gain controller. The analysis can be achieved without constructing a physical network to help evaluate the design. Using the (n, k)-star topology and MAS, the load balancing/restoration problems can be solved much more quickly and accurately compared to other approaches shown in the literature. / Electrical and Computer Engineering

In a large and dense power network, the transmission lines, the generators and the loads are considered to be continuous functions of space. The continuum technique provides a macro-scale analytical tool to gain an insight into the mechanisms by which the disturbances initiated by faults and other random events propagate in the continuum. This dissertation presents one-dimensional and two-dimensional discrete models to illustrate the propagation of electromechanical waves in a continuum system. The more realistic simulations of the non-uniform distribution of generators and boundary conditions are also studied. Numerical simulations, based on the swing equation, demonstrate electromechanical wave propagation with some interesting properties. The coefficients of reflection, reflection-free termination, and velocity of propagation are investigated from the numerical results. Discussions related to the effects of electromechanical wave propagation on protection systems are given. In addition, the simulation results are compared with field data collected by phasor measurement units, and show that the continuum technique provides a valuable tool in reproducing electromechanical transients on modern power systems. Discussions of new protection and control functions are included. A clear understanding of these and related phenomena will lead to innovative and effective countermeasures against unwanted trips by the protection systems, which can lead to system blackouts. / Ph. D.

A new methodology is proposed to investigate the large-signal stability of interconnected power electronics systems. The approach consists of decoupling the system into a source subsystem and a load subsystem, and stability of the entire system can be analyzed based on investigating the feedback loop formed by the interconnected source/load system. The proposed methodology requires two stages: (1) since the source and the load are unknown nonlinear subsystems, system identification, which consists of isolating each subsystem into a series combination of a linear part and a nonlinear part, must be performed, and (2) stability analysis of the interconnected system is conducted thereafter based on a developed stability criterion suitable for the nonlinear interconnected-block-structure model. Applicability of the methodology is verified through stability analysis of PWM converters and a typical power electronics system. / Ph. D.

This thesis investigates the impacts of superconducting magnetic energy storage (SMES) unit on the power system first-swing stability by the impedance model of the SMES unit and EMTP simulations. The impedance model of the SMES unit is established in this thesis for study purpose. It has been concluded that SMES unit can greatly improve the power system first-swing stability. Based on the theoretical analysis and simulation results, the concept of the "Stability Protection Zone" of the SMES unit is proposed. Future work directions are discussed in the conclusion part. / Master of Science