Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

In recent years, direct current power distribution and DC microgrids have gained popularity for a wide range of applications. However, unlike typical AC systems, DC systems must still deal with technical issues such as fault current management/protection, power flow control, power quality management, and the possibility of system instability. The T-type modular DC circuit breaker (T-Breaker) system utilization is proposed in this dissertation as a solution to some of the power quality problems thanks to its compensation capabilities. Inspired by the series and shunt compensation devices in AC transmission and distribution, the T-Breaker device can be utilized in a similar manner to improve the stability in DC grids. Utilizing its modularity feature allows it to be implemented in high voltage DC networks. Its use of locally integrated energy storage and a high tolerance for signal mismatch during quick network transients makes it a distinguished device. When its ancillary compensation functions (shunt, series and series-shunt) are combined with its current breaking function, it can be an all-in-one device that improves future DC grids. This dissertation starts with an overview of the power quality challenges of DC distribution covering the recently proposed solutions to each challenge. The main focus will be on the stability challenges under bus voltage and load power transients when constant power loads (CPLs) are present in the grid. Applications such as electric vehicles, ships, aircrafts and EV charging station contains power electronic converters (dc/dc, dc/ac) that tightly regulate the load, hence they act as CPLs. Due to CPLs' negative incremental impedance, when they interact with the DC system, they might destabilize the grid. Analysis of DC distribution systems's stability has been performed in preliminary studies, and passive stabilization and source/load converter level control strategies have been proposed to address the instability issue, but not (open full item for complete abstract)

Committee: Jin Wang (Advisor) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

Direct current power distribution and dc microgrids have been gaining momentum in recent years for various applications. However, compared to traditional ac systems, dc systems still need to address technical challenges such as fault current management/protection, power flow control, power quality management, and potential system instability. This dissertation proposes the T-Breaker system seeking to address these issues in an all-in-one device with modular multilevel converter functions. It is characterized by its use of locally integrated energy storage, high scalability, and high tolerance to control signal mismatch during the fast network transients. This is a paradigm shift from traditional solid-state circuit breakers as the proposed T-Breaker not only protects against faults, but can also function as an energy router with unparalleled ancillary functions for dc grids. This dissertation starts with a systematic overview of the remaining challenges of dc distribution covering the existing dc circuit breaker technologies, particularly on solid-state circuit breakers, as well as the needs and current status of compensation in dc networks. Taking inspiration from the series and shunt compensation devices in ac transmission and distribution systems, the T-Breaker system with half-bridge sub-modules is derived from traditional solid-state circuit breakers. The proposed circuit has modular multilevel converter functions with an increased number of active switches but no conduction loss penalty when compared with traditional solutions. The basic operation modes and the circuit analysis are carried out, and the limitations are identified for the half-bridge T-Breaker. In order to improve upon these drawbacks, the full-bridge T-Breaker is proposed, with improved performance in sub-module voltage injection to the line, and lowering of total heat flux for more compact thermal designs. Along with the basic functionalities of both T-Breaker topologies, the series and (open full item for complete abstract)

Committee: Jin Wang (Advisor); Vadim Utkin (Committee Member); Julia Zhang (Committee Member) Subjects: Electrical Engineering

Master of Sciences, Case Western Reserve University, 2022, EECS - System and Control Engineering

Voltage regulation and power sharing are the most common problems in DCMGs, and considerable research has focused on the development of techniques to solve these two problems. A hierarchical controller is proposed in this work to enhance the performance of the primary controller to dynamically manage voltage and power in the DCMG. A consensus algorithm is implemented in this work, so that the converters in the DCMG can exchange data through a communication matrix to achieve the desired level of performance. A MATLAB simulation of a DCMG has been developed to represent the 12V DCMG testbed at Case Western Reserve University that has a ring structure. The loads include both constant power loads and constant impedance loads. The performance of the system with primary and secondary control is investigated under different operational scenarios that includes different combinations of loads and different levels of solar power injection into the DCMG.

Committee: Kenneth A. Loparo (Advisor); Vira Chankong (Committee Member); Wei Lin (Committee Member) Subjects: Electrical Engineering

Master of Sciences, Case Western Reserve University, 2016, EECS - System and Control Engineering

As the practicality of decentralized generation progresses, the control and mitigation techniques of the large centralized energy grid become unsuitable solutions for power distribution. The creation of autonomous control on a dc microgrid is necessary to manage the system objectives of the future power grid. In order to begin this study, control algorithms must be tested in both software and hardware experiments. This research will explore the control efficacy of supporting the system objectives on a lab-scale dc microgrid, using a hierarchical control algorithm. The algorithm will determine the network topology of the system, as well as distribute power to the loads in order of priority.

Committee: Kenneth Loparo PhD (Advisor); Mingguo Hong PhD (Committee Member); Marc Buchner PhD (Committee Member) Subjects: Electrical Engineering; Systems Design

Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering

This dissertation presents a hybrid large scale system model of a DC microgrid, its input to state stability analysis and an optimal control algorithm for load side energy management. The theoretical principles of hybrid large scale system modeling, stability, and optimal control for stochastic systems are applied to DC microgrid designed for a photovoltaic based charging station at a workplace parking garage. The example DC microgrid has two energy sources (renewable energy source and power grid) and many plug-in electric vehicle (PEV) charging stations. Stochastic inputs to the system are solar power and charging demand of the PEVs and the control inputs are the vehicle charging power and duration. The hybrid large scale system model of the DC microgrid is developed in state space form to model the large number of DC-DC converters and discrete changes in the system configurations caused by actions of a supervisory controller and converter operating modes. Stability analysis of the model using the Gersgorin principle, an eigenvalue inclusion theorem and connective stability principles provide design guidelines and conditions on interconnection properties. Necessary conditions for the large scale system stability are provided using eigenvalue analysis. The input to state stability analysis is performed using Lyapunov theory for hybrid systems to provide constraints on the dwell time of the switching signal. The optimization problem is structured as an inventory control problem and solved using dynamic programming with stochastic inputs to find the charging power of all the vehicles at each time step. A simple but realistic rule based algorithm is developed to distribute the total charging power among available vehicles. The control algorithm schedules PEV charging power to maximize the use of solar energy, reduce energy taken from the grid, and satisfy the charging demand of all vehicles within the switching constraints. Finally, this research is accompanied by th (open full item for complete abstract)

Committee: Stephen Yurkovich PhD (Advisor); Giorgio Rizzoni PhD (Committee Member); Jin Wang PhD (Committee Member) Subjects: Alternative Energy; Economics; Electrical Engineering; Energy