Browsing by Author "Mesut E. Baran, Committee Member"

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Development and Application of the Light Triggered Emitter Turn-Off (LT-ETO) Thyristor
(2008-05-06) Chen, Bin; Donald Warsing, Committee Member; John J. Grainger, Committee Member; Subhashish Bhattacharya, Committee Member; Mesut E. Baran, Committee Member; Alex Q. Huang, Committee Chair
The performance of a power semiconductor device greatly determines the possible advancements of power electronics systems in regard to efficiency, volume, reliability, cost, cooling method, and even circuit topology. An advanced high power semiconductor device, the Emitter Turn-Off (ETO) thyristor, has been demonstrated to improve the performance of silicon thyristor-based high power devices. The Light Triggered Emitter Turn-Off (LT-ETO) thyristor was subsequently developed, which resulted in an optically controlled power device with excellent static and dynamic performance and expanded functionality through integrated sensors. This dissertation analyzes the design and verifies the performance of the LT-ETO. Conventional high power semiconductor devices require dedicated external power supplies with isolation capability. In contrast, the LT-ETO power switch is optically controlled, a capability not currently available in other commercial high power switches. Optical control greatly simplifies high power converter construction and lowers the overall cost of the system. The developed LT-ETO has been verified in converter circuits. If used in a pulse width modulation (PWM) voltage source converter (VSC), there is no minimum PWM carrier frequency or load current limitation for the LT-ETO if the VSC modulation frequency is greater than several Hz. The LT-ETO-based solid-state circuit breaker (SSCB) and solid-state fault current limiter (SSFCL)—which benefit greatly from the LT-ETO's high current interruption capability—optical control interface, and built-in sensors, are proposed. Comprehensive investigation of the LT-ETO as an AC switch is part of this research. A discussion of innovative methods to achieve complete sensor integration in the LT-ETO is also included in this research. The voltage, current, and temperature sensors are integrated in the device itself for the first time, another capability not currently available in other commercial high power switches. Conventional converters rely on expensive external sensors to gather the voltage, current, and temperature information; but the LT-ETO converter can utilize built-in sensors for protection and close-loop control. The experimental results show that the built-in sensors are very precise and the protection functions can effectively protect the LT-ETO and the converter in a timely manner. Through modeling and analysis, methods to improve the series operation of the LT-ETO are also proposed. Firstly, the static voltage balance is analyzed, and then a compensated gate driver is proposed to improve the dynamic voltage balance. Experimental results demonstrate excellent dynamic voltage balance of the LT-ETO in series operation using only a very small RC snubber. Finally, an active control gate driver method is proposed to automatically achieve dynamic voltage balance by utilizing the LT-ETO's built-in voltage sensor.
High Performance Integrated Controller with Variable Frequency Control for Switching DC-DC Converters
(2007-11-01) Duan, Xiaoming; Alex Q. Huang, Committee Chair; Kevin G. Gard, Committee Member; Maysam Ghovanloo, Committee Member; Mesut E. Baran, Committee Member
Development of digital core chips poses serious challenges to the power supply design. High performance switching DC-DC converter must meet requirements of high current, low voltage tolerance, fast transient response, high power efficiency, small profile and low cost. The conventional PWM control with constant switching frequency has limitation to improve both transient response and power efficiency because there is a conflicting requirement on switching frequency. The control scheme with variable frequency has promising features to achieve better overall performance, but the issues in the reported design approaches limit their usefulness in the practical applications. This dissertation reviews and summarizes the issues and the design considerations in the high current switching DC-DC converters. To improve the system performance, novel control architecture with variable switching frequency and novel implementation of the integrated controller are proposed in this dissertation. The proposed control architecture is modeled and analyzed. Fully differential circuits are designed to implement the control core functions. The design methodology and the design considerations are discussed. The control concept and the proposed circuits are verified by the prototype controller chip.
Power System Dynamic Voltage Management with Advanced STATCOM and Energy Storage System
(2007-12-19) Han, Chong; Subhashish Bhattacharya, Committee Member; Mo-Yuen Chow, Committee Member; Mesut E. Baran, Committee Member; Tomislav Vukina, Committee Member; Alex Q. Huang, Committee Chair
STATCOM (static synchronous compensator) and ESS (energy storage system), as a shunt-link flexible AC transmission system (FACTS) controller, has shown extensive feasibility in terms of cost-effectiveness in a wide range of problem-solving abilities from transmission to distribution levels. Recently, advances in power electronics technologies, such as the emerging kilohertz high power semiconductor switches, cascaded multilevel converter (CMC) topology comprising modular H-bridge voltage source converter (VSC), and digital control technology, have the potential to achieve the modularity and scalability design, lower the overall cost, and improve the reliability and functionality of power electronics-based controllers, hence, resulting in increasing applications of STATCOM⁄ESS. However, how to control a CMC-based STATCOM⁄ESS to realize excellent performance, high reliability and low cost poses the challenges to researchers. On the other side, renewable large wind farms, as a fast growing power generation method, undergoes its inherent power quality and stability issues. How to develop the effective and accurate model of a wind power system and how to control STATCOM for wind power support are not in a classical textbook and posing challenges. Meanwhile, as an industrial customer of utilities, electrical arc furnace (EAF) is the major flicker source that degrades the grid power quality. How to economically and efficiently mitigate EAF flicker is a tough issue bothering utility professionals. As a promising solution, a high bandwidth STATCOM⁄ESS can be used. This dissertation is dedicated to a comprehensive study of CMC-based STATCOM and its ultracapacitor energy storage system (UESS), and its applications in power system dynamic voltage management, specifically, wind farm voltage fluctuations suppressions and EAF flicker mitigation. The goal of this dissertation is to achieve high-performance, reliable, flexible, cost-effective controllers of the CMC-based STATCOM⁄UESS for the specific challenging utility applications. Major contributions proposed in this dissertation include: 1) STATCOM model analysis and compensator design guideline; 2) STATCOM AC-side energization and de-energization; 3) STATCOM per-phase DC voltage balancing; 4) wind farm voltage fluctuation suppression; 5) EAF flicker mitigation; 6) modeling, integration and control of UESS.