No description available.

No description available.

No description available.

No description available.

The use of high power converters has increased tremendously. Increased demand for transportation, housing and industrial needs means that more number of power converters interact with the utility power grid. These converters are non-linear and they draw harmonic currents, significantly affecting power quality. To reduce harmonics, filters, power factor correction circuits and capacitor banks are required. And the development of hybrid technologies and renewable energy power stations trigger a demand for power converters with bi-directional capabilities. The objective of this thesis is to develop a high power quality, bi-directional AC-DC power converter that is a solution to the aforementioned problems. This thesis studies an existing topology for a high power AC-DC power conversion with transformer isolation. The topology consists of an uncontrolled rectifier followed by a DC-DC converter to produce a set voltage output. A design example of the topology is simulated using the PSIM software package (version 6). Critical performance characteristics such as power factor and total harmonic distortion are analyzed. Following that study a new topology is proposed, which is an improvement over the older design, with reduced power conversion stages. The new topology has a fully controlled current source Pulse Width Modulation (PWM) rectifier at the front end to replace the uncontrolled rectifier and DC-DC combination. This topology has multiquadrant operational capabilities and the controller employs Selective Harmonic Elimination techniques to produce the programmed PWM switching functions for the rectifier. A design example of the converter and the digital controller are simulated in PSIM environment. The converter input current THD (Total Harmonic Distortion) and input power factor are within IEEE 519 and DoE standards. The converter is simulated in both first and fourth quadrant operations. A side-by-side comparison of the two topologies is done with respect to design and performance features such as power factor, THD, filter size, etc. The new topology converter provides performance superior to that of the older topology. Finally the thesis explores possible applications for the converter in power supplies, renewable energy and hybrid technologies.

No description available.

Multi-pulse converters have been widely used for a multi-megawatt scale power generating system to comply with harmonic regulations. Among all types of multi-pulse converters, a 12-pulse converter is the most widely used due to the simple structure, which consists of a delta-delta and a delta-wye phase-shift transformer pair and it effectively mitigates undesirable harmonics from the nonlinear load. In the early 2000s, a shunt type passive front-end for a shipboard power system was proposed. By shunting the two gensets with 30° phase angle difference, a single phase-shift transformer effectively eliminates 5th and 7th harmonics. It achieves a significant size and weight reduction compared to a 12-pulse converter while keep the comparable harmonic cancellation performance. Recently, a hybrid type front-end was proposed. On top of the passive front-end, 3 phase active power filter was added and an additional harmonic cancellation was achieved to further eliminate 11th and 13th harmonics. However, the performance of both the passive and hybrid type front-end are highly dependent on the size of the line reactor in ac mains. A back to back active power filter is proposed in this dissertation to replace the phase-shift transformer in the multi-generator power architecture. The proposed front-end does not include phase-shift transformer and the size and the weight of the overall front-end can be significantly reduced. Due to the active harmonic compensation, the back to back front-end achieves better power quality and the line reactor dependency is improved. The number of required dc-link capacitors is reduced by half by introducing a back to back configuration and the capacitor size is reduced by adjusting the phase angle difference of genset to cancel out the most significant voltage harmonics in the shared dc-link bus. The overview of the existing shunt type front-end is provided and the concept of back to back active power filter is validated by simulation and prototype hardware. The comparison between existing front-end and the proposed front-end is provided to highlight the superior performance of back to back active front-end. The dc-link bus current and voltage ripple analysis is provided to explain the dc-link ripple reduction mechanism. / Doctor of Philosophy / The transportation electrification has gained more and more attention due to its smaller carbon dioxide emission, better fuel efficiency. The recent advances in power devices, microcontrollers, and transducers accelerate the electrification of transportation. This trend is shown in the propulsion system in marine transport as well and the electric propulsion system has been widely used to meet the strict environmental regulations. However, the non-linear circuit components such as capacitor and diode in the electric propulsion system draw non-linear current and significantly deteriorate power quality and lead to critical problems such as reduced life span of circuit components Accordingly, a front-end is required to improve power quality. Also, it is desired to have compact and lightweight front-end for installation flexibility and fuel efficiency improvement. In this dissertation, several front-ends using a phase-shift transformer are reviewed and a detailed analysis is provided to help understand the harmonic cancellation principle of the existing front-end through equivalent circuit analysis, quantitative analysis, and a phasor diagram representation. Based on the analysis of the existing front-ends and shipboard power architecture, lightweight and high-performance front-end is proposed and verified by simulation and prototype hardware. The performance, size comparison between existing front-end and the proposed front-end is provided to show the advantage of the proposed front-end.

This research work is devoted to the analysis, design and development of the first medium power Current-Source Converter (CSC) based distribution-type Static Synchronous Compensator (D-STATCOM) with simplest converter topology and coupling transformer connection. The developed CSC-D-STATCOM includes a +/-750kVAr full-bridge CSC employing Selective Harmonic Elimination Method (SHEM), a 250kVAr low-pass input filter at 1kV voltage level, and a &amp / #916 / /Y connected coupling transformer for connection to medium-voltage load bus. The power stage of CSC is composed of series connection of natural air-cooled high-voltage IGCT switched at 500 Hz for the elimination of four lowest current harmonic components (5th, 7th, 11th, 13th), and optimized fast recovery high voltage diode in each leg. Reactive power control is achieved by applying the phase shift angle control at fixed modulation index, which is implemented digitally on a DSP microcontroller. The developed system has been implemented for compensation of rapidly varying reactive power demand of coal mining excavators in Turkish Coal Enterprises. The field test results have shown that the proposed CSC D-STATCOM serves as a technologically new full substitute of conventional Voltage-Source Converter based D-STATCOM having complex transformer connections in view of relatively fast response in reactive power compensation, very low total demand distortion factors, complying with the IEEE Std. 519-1992 even for the weakest power systems, and acceptable efficacy figures.

Submitted by Maria Suzana Diniz (msuzanad@hotmail.com) on 2015-11-05T13:46:16Z No. of bitstreams: 1 arquivototal.PDF: 4508623 bytes, checksum: 8e1affd5d5c342bcac7e265720885b0c (MD5) / Made available in DSpace on 2015-11-05T13:46:16Z (GMT). No. of bitstreams: 1 arquivototal.PDF: 4508623 bytes, checksum: 8e1affd5d5c342bcac7e265720885b0c (MD5) Previous issue date: 2015-07-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work presents an active power filter for three-phase three-wire systems without an inductor when compared to the usual structure of a shunt active power filter. For the determination and control of the references it was used the Park’s transformation, it means that all control was done in synchronous axes. The active filter of this work is in parallel configuration acting therefore as a current source and should correct the power factor and current harmonics selectively of the power grid. Simulation results were presented validating the control strategy. / Neste trabalho é apresentado um filtro ativo de potência trifásico para sistemas a trifásicos a três fios com um indutor a menos em comparação com a estrutura usual de um filtro ativo shunt. Para a determinação das referências e controle foi utilizada a transformada de Park, ou seja, todo o controle foi feito em eixos síncronos. O filtro ativo deste trabalho está na configuração paralela funcionando, portanto, como uma fonte de corrente e deverá corrigir o fator de potência e harmônicos de corrente da rede elétrica, estes últimos de forma seletiva. Foram apresentados resultados de simulação validando a estratégia de controle.

No description available.