Modelling and Control of Switched Reluctance Machines

Today, switched reluctance machines (SRMs) play an increasingly important role in various sectors due to advantages such as robustness, simplicity of construction, low cost, insensitivity to high temperatures, and high fault tolerance. They are frequently used in fields such as aeronautics, electric and hybrid vehicles, and wind power generation. This book is a comprehensive resource on the design, modeling, and control of SRMs with methods that demonstrate their good performance as motors and generators

Modelling and Control of Switched Reluctance Machines

Today, switched reluctance machines (SRMs) play an increasingly important role in various sectors due to advantages such as robustness, simplicity of construction, low cost, insensitivity to high temperatures, and high fault tolerance. They are frequently used in fields such as aeronautics, electric and hybrid vehicles, and wind power generation. This book is a comprehensive resource on the design, modeling, and control of SRMs with methods that demonstrate their good performance as motors and generators

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Modelling and Control of Switched Reluctance Machines

Today, switched reluctance machines (SRMs) play an increasingly important role in various sectors due to advantages such as robustness, simplicity of construction, low cost, insensitivity to high temperatures, and high fault tolerance. They are frequently used in fields such as aeronautics, electric and hybrid vehicles, and wind power generation. This book is a comprehensive resource on the design, modeling, and control of SRMs with methods that demonstrate their good performance as motors and generators

Development of a current limiting solid-state circuit breaker based on wide-band gap power semiconductor devices for 400V DC microgrid protection

Popularity of DC distribution systems is increasing for many residential and industrial applications such as data centres, commercial and residential buildings, telecommunication systems, and transport power networks etc. Compared to AC systems, they have demonstrated higher power efficiency, less complexity, and more readiness of integrating with various local power sources and DC electronic loads. However, one of the major technical issues hindering this trend is the lack of effective DC fault protection devices/circuits. Although conventional electromechanical circuit breakers work well in AC systems, they are not suitable for DC systems due to their long response time (ranging from tens of milliseconds to hundreds of milliseconds). Such a long response time is far beyond the withstand time (typically tens of microseconds) of most power electronic devices in short-circuit operating conditions. In contrast, Solid-State Circuit Breakers (SSCBs) are able to offer ultrafast switching speed thanks to the modern power semiconductor devices which can turn off in microseconds or even in tens of nanoseconds. Furthermore, the ever-increasing fault current level in DC systems poses a significant mechanical and thermal stress on the whole DC system. Therefore, the desire for the protection devices with the feature of fast switching speed along with the current-limiting capability has prompted intensive research in this area over the last decade in both academia and industry. However, the relatively high conduction losses and limited short-circuit capability are two of the major drawbacks of SSCBs. With the growing maturity and increasingly commercial availability of Wide-Bandgap (WBG) semiconductor devices, a SSCB based-on WBG devices is a promising solution to alleviate the issues since WBG semiconductors have demonstrated superior material properties over the conventional silicon material such as lower specific on-resistance, higher junction temperatures and higher breakdown voltage. This research aims to design and develop a WBG-based solid-state circuit breaker for a 400V DC microgrid application. To accomplish this task, this work starts with a comprehensive review of DC microgrid technology followed by an extensive review of the state-of-the-art DC circuit breakers. Then, to develop a circuit topology for the proposed SSCB, a practical current limiter is analysed, simulated, and evaluated. Based on this topology, the proposed SSCB is configured with a high-voltage normally-on Silicon Carbide Junction Field Effect Transistors (SiC-JFETs) cascading a low-voltage normally-off power MOSFET. This solution offers several advantages. For example, it does not require any additional sensing and tripping circuitry for short-circuit protection and therefore has a fast response speed. Meanwhile, the use of power SiC JFETs tends to reduce the conduction losses and enhance the short-circuit robustness of SSCBs. In addition, it offers the feature of current limiting which could ease the thermal and mechanical stresses on the whole DC system. The operating process of the proposed SSCB is analysed and the analytical results are compared with the simulated results; In the end, a prototype SSCB has been built and evaluated for short-circuit protection in a 400V DC system. In addition, to effectively suppress the overvoltage at the turn-off of SSCBs, a novel hybrid snubber circuit has been proposed by taking into account the advantages offered by both conventional Resistor-Capacitor-Diode (RCD) snubbers and Metal-Oxide Varistors (MOVs). Finally, other functions of the proposed SSCBs including overload protection, over temperature protection and protection coordination have been investigated and some operating issues such as false tripping and SSCB reset have been addressed

Advances in hybrid water-lubricated journal bearings for use in ocean vessels

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 439-441).The outboard bearings that support shafts in naval ships and submarines present unique challenges to designers, shipbuilders, and operators. Such bearings must operate continuously and reliably in demanding environments at speeds that vary from below 1 rpm to well over 100 rpm. Water-lubricated bearings typically used for these applications operate hydrodynamically and are prone to adverse effects at lower speeds such as increased abrasive and adhesive wear as well as stick-slip shaft motion. This project focuses on developing a hybrid journal bearing capable of operating with hydrostatic pump pressure at lower rpm, while still maintaining the capability for hydrodynamic operation at higher rpm. Benefits of such a system include extending the periodicity between outboard bearing replacements, less abrasion and scoring damage to the propulsion shaft, and preventing stick-slip shaft motion. To enable the in-water replacement of bearings without removal of the propulsion shaft, a partial arc (<180 degree wrap) configuration is required. This partial arc constraint introduces several unique manufacturing difficulties. To address this, a novel manufacturing process has been developed that enables the rapid fabrication of high precision bearings with diameter and roundness errors of less than 0.001" (25.4 microns) on a nominal diameter of 3.24" as measured with a Coordinate Measuring Machine - greatly exceeding the published tolerances of conventional methods. A unique experimental test rig was designed and built in order to measure the performance of 15 different prototype bearing designs. The rig is capable of submerged bearing testing in both hydrostatic and hydrodynamic modes of operation, with fundamental parameters such as speed, torque, loads, pressures, flow rates, and shaft position recorded. The operating characteristics of the bearings were then analyzed to identify key features and variables affecting bearing performance. Certain bearing designs were found to be inherently stable for side loading conditions, without the use of compensation typically used in hydrostatic bearings. This finding led to bearings designed with simplified hydrostatic features and fluid supply systems. Such designs were found to have minimal degradation in hydrodynamic performance, making them particularly suitable for use as hybrid bearings. The key design drivers identified in this work are combined with ancillary factors to discuss the feasibility of hybrid bearings for use in marine applications.by Brian Douglas Heberley.Ph.D