The integrated high-quality rectifier-regulators [1] are not practical for universal input voltage and wide load range applications because of high bulk-capacitor voltage stress at lighter loads. This load-dependent characteristic of the bulk-capacitor voltage is due to the integration of a discontinuous conduction mode boost converter and a continuous conduction mode dc-dc converter. In addition, this power factor correction technique suffers from a high-voltage spike on the switch at turn-off. In this thesis, variable frequency control, swinging choke, and low loss LC snubber techniques are proposed to alleviate these problems. Finally, several experimental converters with different specifications are evaluated with respect to efficiency and ability to meet the IEC555-2 standards. / Master of Science

A novel, zero-current-transition (ZCT) topology of the single-switch three-phase boost PFC rectifier is proposed. The soft transition is achieved with a low-power auxiliary circuit employing an additional switch. The circuit can be used with an IGBT at switching frequencies up to 50. Its operation is analyzed in detail, and design guidelines are provided. The small signal model of the circuit is developed, and voltage mode control is designed. The results are verified on a 4 kW, 50 kHz, experimental ZCT rectifier with an IGBT; total harmonic distortion below 9% and efficiency above 95% were obtained. / Master of Science

From the early days of HVDC system applications, the importance of mathematical modelling of the dynamics of Line Commutated Converter (LCC) HVDC systems has been appreciated. There are essentially two methodologies used to develop mathematical models of dynamic systems. One methodology is to define the properties of the system by the “laws of nature” and other well-established relationships. Basic techniques of this methodology involve describing the system’s processes using differential equations. This methodology is called “Deductive Modelling”. The other methodology used to derive mathematical models of a dynamic system is based on experimentation. Input and output signals from the original system are recorded to infer a mathematical model of the system. This methodology is known as “Inductive Modelling”. A review of the current state of the art of modelling LCC HVDC systems indicates that majority of the techniques utilized to develop mathematical models of LCC HVDC systems have used the “Deductive Modelling” approach. This methodology requires accurate knowledge of the ac systems and the dc system and involves complicated mathematics. In practice, it is nearly impossible to obtain accurate knowledge of the ac systems connected to LCC HVDC systems. The main aim of this thesis is to present an “Inductive Modelling” methodology to calculate the plant transfer functions of LCC HVDC systems. Due to the uncertain nature of the effective short circuit ratio of rectifier and inverter converter stations, generic ranges of parametric uncertainties of the developed plant transfer functions were determined. Based on the determined range of HVDC plant parametric uncertainty, Quantitative Feedback Theory (QFT) methodology was used to design the parameters of the LCC HVDC control system. The stability of the start-up and step responses for varying ac system conditions validated the “Inductive Modelling” technique and the QFT design methodology. The thesis presents the following, which are considered to be scientific advancements and contributions to the body of knowledge: · Novel LCC HVDC Step Response (HSR) equations were developed using an “Inductive Modeling” technique. · The range of parametric variations of the LCC HSR equations were determined for various rectifier and inverter ac system effective short circuit ratios. · The LCC HSR equations were used to develop the LCC HVDC plant transfer functions for various rectifier and inverter effective short circuit ratios. · The LCC HVDC plant transfer functions were utilized to design an LCC HVDC control system for varying ac system conditions using Quantitative Feedback Theory (QFT) methodology. The main contributions of this thesis relate to LCC HVDC systems. This thesis does not attempt to advance control theory however this thesis does apply existing classical control theory to LCC HVDC control systems. Index Terms: Line Commutated Converter, HVDC, inductive modelling, power system, transient analysis. / Thesis (Ph.D.)-University of KwaZlu-Natal, Durban, 2011.

During the past two decades, Quality of Supply has become a serious problem for Variable Speed Drives in the industrial and commercial sectors. Quality of Supply problems can trip Variable Speed Drives, which results in loss of production, which is a significant problem in the paper and pulp industry. Researchers have proposed that Quality of Supply problems can be minimised in-house, using controlled front end rectifiers (boost rectifier), to maintain a regulated DC link voltage in the Variable Speed Drive configuration, as most faults are created by a varying supply voltage. This thesis extends the work performed on boost rectifiers by investigating the feasibility of replacing the classical controllers with a Continual Online Trained Artificial Neural Network current controller. The approach adopted in this thesis was to evaluate and extend the work previously performed on conventional boost rectifier current controllers and Continual Online Trained Artificial Neural Network current controlled inverter, at the University of Natal. During this evaluation, the respective controller shortcomings were identified and addressed. Thereafter the Continual Online Trained Artificial Neural Network current controller was modified, according to the control requirements of the boost rectifier, and used as a replacement for the conventional current controller in the boost rectifier system. Finally, the Continual Online Trained Artificial Neural Network current controller was evaluated to assess its viability as a current controller for a boost rectifier. The concept of implementing the real-time Continual Online Trained Artificial Neural Network current controller using a DSP (Digital Signal Processor) was described, along with the main features and practical limitations of existing commercial DSP's. It is shown that at the time of writing of this thesis, the commercially available DSP' s are not powerful enough to implement the Continual Online Trained Artificial Neural Network current controller. However this thesis also shows that it is feasible to implement the real-time controller on the newly released TMS320C67 DSP card. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Thesis (Ph. D.)--Ohio University, August, 1993. / Title from PDF t.p.

This thesis presents a multi-stage rectifier for wireless power transfer in biomedical implant systems. The rectifier is built using Schottky diodes. The design has been simulated in 0.5µm and 130nm CMOS processes. The challenges for a rectifier in a wireless power transfer systems are observed to be the efficiency, output voltage yield, operating frequency range and the minimum input voltage the rectifier can convert. The rectifier outperformed the contemporary works in the mentioned criteria.

High conversion efficiency and fast transient response at high switching frequency are the two main challenges for low-voltage high-current DC-DC converters, which are the motivations of the dissertation work. To reduce the switching power loss, soft switching is a desirable technique to keep power loss under control at high switching frequencies. A Duty-Cycle-Shift (DCS) concept is proposed for half-bridge DC-DC converters to reduce switching loss. The concept of this new control scheme is shifting one of the two symmetric PWM driving signals close to the other, such that ZVS can be achieved for the lagging switch due to the shortened resonant interval. By applying a basic DCS concept to a conventional half-bridge DC-DC converter, Zero-Voltage-Switching is achieved for one of the two primary switches. To achieve ZVS for the other switch, a ZVS half-bridge topology is proposed. Basically, by adding an active branch to the conventional half-bridge topology, the leakage inductance energy is trapped during the freewheeling time, and the energy is released to achieve ZVS for the other switch. In addition, a modified ZVS half-bridge topology is proposed to ground the auxiliary switch, and thus, a simple drive circuitry can be applied to the auxiliary switch. Leakage inductance leads to ringing issue in a half-bridge DC-DC converter. An active-clamp snubber topology is presented in the half-bridge DC-DC converters to recycle the leakage inductance energy and attenuate the ringing. Since dissipative snubbers are removed, a converter can operate more efficiently. Body-diode reverse-recovery-related loss in SRs increases with the switching frequency. To reduce this reverse-recovery loss, two passive snubber circuits are proposed for SR rectifiers in a current dubler rectifier. The proposed snubbers attenuate reverse recovery ringing and higher efficiencies are achieved. A unified DC model is derived based on the state-space average equation, which is suited for both symmetric and asymmetric half-bridge DC-DC converters. Furthermore, the DC analysis is conducted based on the unified DC model for symmetric and asymmetric half-bridge DC-DC converters with current-doubler rectifier. The AC model of isolated DC-DC converters is also established, and output impedance is analyzed for the purpose of transient response investigation. A two-stage approach is a trade-off between conversion efficiency and fast transient response. Full-Duty-Cycle (FDC) two-stage architecture is proposed to achieve desirable open-loop output impedance and fast transient response. Class-D resonant converters are investigated and recognized as potential topologies to reduce switching loss and SR conduction loss. Considering the limited regulation capability of class-D resonant converters, low-Q SRC and LLC resonant converters are proposed as candidate topologies in two-stage approaches.

Simulations of two types of constant-frequency resonant power converters using SPICE-2/I-G SPICE are performed. The first one is a parallel resonant converter (PRC) using a controlled output rectifier. The PRC is operated at a constant frequency and its output voltage is regulated by controlling the firing angle of the output rectifier. The other circuit is the phase-controlled dual resonant converter (DRC) which employs two PRCs with their output (Capacitor voltages) connected in series. In the scheme, again the PRCs are operated at a constant frequency. By controlling the phase delay of the two PRCs, regulation of the output voltage is achieved. The behaviors of these two types of constant frequency resonant converters have been analyzed in details recently by Tsai and documented in his thesis. The objectives of the present work is to verify some of Tsai's key findings via computer simulations. First of all, the DC output characteristics of the parallel resonant converter (PRC) using the conventional acontrol (phase control) scheme and the new a-control scheme are simulated. The a-control scheme is implemented by monitoring the delay angle of the output controlled rectifier and the zero-crossing of the resonant capacitor voltage waveform while the a control is implemented by monitoring the delay angle of the output controlled rectifier with respect to the switching instance of the input inverter. The current and voltage ratings of different circuit components as a function of the control parameter-a angle are shown. The control-to-output characteristics are verified. The advantages of acontrol scheme is demonstrated. Simulation results of the phase-controlled dual resonant converter (DRC) are presented under various operating conditions. A comprehensive understanding of the behavior complex of the DRC are obtained. The ability to regulate the link voltage of the DRC is demonstrated. Boundary conditions of the DRC for natural commutation ( line or load) of the power devices are also verified. Some comments on SPICE-2/I-G SPICE simulation of the resonant circuits are presented. / M.S.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 6, 2009). Thesis advisor: Dr. Naz E. Islam. Includes bibliographical references.

Orientador: Ennio Peres da Silva / Dissertação ( mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-17T04:55:49Z (GMT). No. of bitstreams: 1 Gambetta_Francielle_M.pdf: 4780185 bytes, checksum: f2071d96fca67109088a5766792577eb (MD5) Previous issue date: 2010 / Resumo: Para países com disponibilidade de energia elétrica relativamente barata, como o Brasil, o custo de instalação é o fator mais importante para a produção de hidrogênio eletrolítico, representando mais de 50% do custo total. O retificador de corrente é um dos principais equipamentos que compõem um sistema de eletrólise da água e é objeto de estudo desta dissertação. A partir de uma análise técnica, concluiu-se que, atualmente, o sistema de retificação mais adequado ao processo de produção de hidrogênio eletrolítico é o sistema a tiristor, principalmente por apresentar maior eficiência e confiabilidade operacional. Por meio de uma análise de mercado, concluiu-se que o mercado nacional, em sua maioria, está apto a fornecer retificadores industriais apenas para aplicação em eletrolisadores unipolares, já o mercado internacional possui uma vasta gama de retificadores com diversos níveis de tensão e corrente de saída, sendo capaz de fornecer estes equipamentos tanto para alimentar eletrolisadores industriais unipolares quanto bipolares. O custo do hidrogênio foi calculado tomando como base estudos anteriores e utilizando a Energia Vertida Turbinável (EVT) da UHE de Itaipu, o que resultou em US$ 2,66/kg para uma planta com capacidade de produzir 4.365 m3/h de hidrogênio. A influência do custo do retificador sobre o custo de produção é de 10,8% e, assim, uma diminuição de 50% no custo deste equipamento promoveria uma redução de 5,4% no custo do hidrogênio eletrolítico. Apesar de pequena, esta redução pode ser determinante em muitos casos. Assim, a introdução de uma linha de pesquisa em um pólo tecnológico para o desenvolvimento destes equipamentos é interessante, pois além de contribuir com a redução do custo do hidrogênio eletrolítico, representa uma oportunidade de crescimento econômico que pode colocar o Brasil em destaque de forma positiva dentro dos cenários energético e econômico mundiais / Abstract: For countries with relatively cheap electricity availability, such as Brazil, the cost of installation is the most important factor for the production of electrolytic hydrogen, representing more than 50% of the total. The power rectifier is one of the main devices comprising the water electrolysis system and it is the object of study in this dissertation. From a technical analysis, it was concluded that currently the most suitable system for electrolytic hydrogen production is the thyristor system, mainly due to its higher efficiency and operational reliability. Through market analysis, it was concluded that most of rectifiers available in the domestic market are designed only for use in industrial unipolar electrolysers. On the other hand, the international market has a wide range of rectifiers with different levels of voltage and current output, being capable of providing such equipment for both industrial unipolar and bipolar electrolysers. The cost of hydrogen was calculated using previous studies of the Spilled Turbinable Energy (STE) of Itaipu Hydroelectric Energy Plant, and resulted in US$ 2.66/kg for a plant with capacity to produce 4,365 m3/h of hydrogen. The influence of the rectifier cost on the gas production cost is 10.8%, and thus a decrease of 50% in the cost of such equipment would promote a reduction of 5.4% in the cost of the electrolytic hydrogen. Although small, this reduction can be decisive in many cases. Thus the introduction of a research line at a technological center for the development of this equipment is interesting, which also contributes to lowering the cost of electrolytic hydrogen and is an opportunity for economic growth to highlight Brazil in the worldwide energy and economic scenery / Mestrado / Mestre em Planejamento de Sistemas Energéticos