Fault tolerant drives for safety critical applications

PhD ThesisThe correct operation of adjustable speed drives, which form part of a larger system, is often essential to the operation of the system as a whole. In certain applications the failure of such a drive could result in a threat to human safety and these applications are termed 'safety critical'. The chance of a component failure resulting in non-operation of the drive can be dramatically reduced by adopting a fault tolerant design. A fault tolerant drive must continue to operate throughout the occurrence of any single point failure without undue disturbance to the power output. Thereafter the drive must be capable of producing rated output indefinitely in the presence of the fault. The work presented in this thesis shows that fault tolerance can be achieved without severe penalties in terms of cost or power to mass ratio. The design of a novel permanent magnet drive is presented and a 'proof of concept' demonstrator has been built, based on a 20 kW, 13000 RPM aircraft fuel pump specffication. A novel current controller with near optimal transient performance is developed to enable precise shaping of the phase currents at high shaft speeds. The best operating regime for the machine is investigated to optimise the power to mass ratio of the drive. A list of the most likely electrical faults is considered. Some faults result in large fault currents and require rapid detection to prevent fault propagation. Several novel fault sensors are discussed. Fault detection and identification schemes are developed, including new schemes for rapid detection of turn to turn faults and power device short circuit faults. Post fault control schemes are described which enable the drive to continue to operate indefinitely in the presence of each fault. Finally, results show the initially healthy drive operating up to, through and beyond the introduction of each of the most serious faults.EPSR

A study of multiplex data bus techniques for the space shuttle

A comprehensive technology base for the design of a multiplexed data bus subsystem is provided. Extensive analyses, both analytical and empirical, were performed. Subjects covered are classified under the following headings: requirements identification and analysis; transmission media studies; signal design and detection studies; synchronization, timing, and control studies; user-subsystem interface studies; operational reliability analyses; design of candidate data bus configurations; and evaluation of candidate data bus designs

Series connection of power semiconductors for medium voltage applications

The series connection of power semiconductor devices allows the operation at voltage levels higher than the levels allowed by one single semiconductor. However, due to individual parameter differences of the series connected devices it is difficult to ensure a proper voltage balance between the series connected power devices and if any semiconductor exceeds its maximum blocking voltage it will fail. Because of its gate controllability and its low gate energy requirements, the IGBT is the preferred choice when high number of switching devices must be connected in series. In this research work an IGBT gate driver has been developed which will control the behaviour of the IGBT during the switching process. In consequence, this gate driver should ensure a proper voltage balance between the series connected IGBT devices. Basically, this PhD research work deals with the analysis and the modelling of the behaviour of the IGBT / Diode, proposes an active gate control and shows its validity for the series connection of IGBT / Diode devices. Finally, voltage source converter topologies are briefly compared for reactive power compensation applications at Medium Voltage utility grids. The required blocking voltage capacity is achieved by means of the series connection of power semiconductor devices.La conexión en serie de semiconductores de potencia permite trabajar a tensiones de trabajo superiores a las que podría soportar un único semiconductor. Sin embargo, debido a diferencias en las características de los propios semiconductores es difícil garantizar el equilibrado adecuado de las tensiones de trabajo entre los distintos semiconductores conectados en serie. Si algún semiconductor supera su máxima tensión de trabajo este fallará. Debido a su controlabilidad y bajo requerimiento energético por puerta el IGBT es la opción preferida cuando se requiere la conexión en serie de gran cantidad de semiconductores. En este trabajo de investigación se ha desarrollado un driver para IGBT que permita el control del proceso de conmutación del IGBT y garantice el equilibrado de las tensiones entre los IGBTs conectados en serie. Básicamente, en este trabajo de investigación se presenta el análisis y modelado del comportamiento del IGBT/Diodo, el control activo empleado para controlar el proceso de conmutación del IGBT y su validez para la conextión en serie. Finalmente, se presenta una pequeña comparación de convertidores de fuente de tensión para aplicaciones de compensación de energía reactiva conectados directamente a redes de Media Tensión. La capacidad de bloqueo requerida se obtiene mediante la conexión en serie de semiconductores de potencia.Potentzi erdi eroaleen serie elkarketak, erdi eroale batek jasan dezakeena baino tentsio maila altuagoan lan egitea ahalbideratzen du. Hala ere, erdi eroaleen arteko ezaugarri ezberditasunak direla eta, zaila egiten da tentsio banaketa egokia zihurtatzea. Erdi eroaleetariko batek bere gehienezko tentsio maila gainditzen badu honek huts egingo du. Erdi eroale asko seriean elkartu behar direnean IGBT-a izaten da aukerarik hobetsiena bere kontrolagarritasuna eta behar duen ateko energia maila baxua dela eta. Ikerketa lan honetan IGBT baten ateko “driver”-a garatu da. Honek IGBT-aren konmutazio prozesua kontrolatu behar du eta aldi berean, seriean elkarturiko IGBT-en artean, tentsio banaketa egokia lortu. Funtsean, ikerketa lan honetan IGBT eta Diodo-aren analisia eta modelatua erakusten dira. Modu berean “driver”-ean erabilitako kontrola eta bere baliozkotasuna IGBT/Diodo-en serie elkarketarako erakusten dira. Azkenik, Tentsio Ertaineko sarera zuzenean konektaturiko Tentsio Iturri Bihurgailuen arteko konparaketa bat egin da. Sareko tentsio maila altua dela eta erdi eroaleen serie elkarketa derrigorrezkoa da

Self-Checking Ripple-Carry Adder with Ambipolar Silicon Nanowire FET

For the rapid adoption of new and aggressive technologies such as ambipolar Silicon NanoWire (SiNW), addressing fault-tolerance is necessary. Traditionally, transient fault detection implies large hardware overhead or performance decrease compared to permanent fault detection. In this paper, we focus on on-line testing and its application to ambipolar SiNW. We demonstrate on self - checking ripple - carry adder how ambipolar design style can help reduce the hardware overhead. When compared with equivalent CMOS process, ambipolar SiNW design shows a reduction in area of at least 56% (28%) with a decreased delay of 62% (6%) for Static (Transmission Gate) design style