This thesis presents a new DC/AC inverter circuit which is based on a switched-capacitor circuit topology with reduced components (power switch and capacitor) count for low power applications. The proposed circuit has distinct features of both voltage boost-up and near sinusoidal (multi-level/staircase) AC output voltage. The main idea is to utilise a simple circuit technique called resonant-based Double Switch Single Capacitor Switched-Capacitor (DSSC SCC) with variable duty cycle Pulse Width Modulation (PWM) control technique in such a way that multi-level voltage can be realised across a capacitor. In order to show the superiority of the applied technique, comparisons with other techniques/circuits configurations are presented. The circuit technique can significantly reduce the number of multiple stages of switched-capacitor circuit cells of the recent switched-capacitor multi-level inverter topology. The proposed inverter (with integrated DSSC SCC technique) can generate a line-frequency with 13-levels near sinusoidal AC output voltage with low total harmonics distortion. The output voltage can be achieved with the least number of components use and only a single DC source is used as an input. The proposed inverter topology is also reviewed against other inverter-based switched-capacitor circuit topology and the well-known multi-level inverter topology. The proposed inverter has shown a tremendous reduction in the total harmonics distortion and circuit component count in comparison with the recent Switched-Capacitor Boost multi-level inverter and the classical Cascaded H-Bridge multi-level inverter. Mathematical analysis shows the design of the proposed inverter and PSPICE simulation result to verify the design is also presented. The practical experiment implementation of the proposed system is presented and proves the correct operation of the proposed inverter topology by showing consistency between simulation results and practical results.

A instalação de geração distribuída nas redes de distribuição e de subtransmissão de energia elétrica tem apresentado significativo crescimento em âmbito mundial, impulsionada pelos benefícios que pode proporcionar aos sistemas elétricos, pela necessidade de diversificação da matriz energética dos países, pela desregulamentação do setor de energia elétrica em diversos países e pela necessidade de gerar energia elétrica de forma sustentável. No entanto, para que os geradores distribuídos possam de fato beneficiar a operação das redes elétricas, seus impactos técnicos devem ser cuidadosamente estudados, sobretudo em redes de distribuição, as quais foram inicialmente planejadas para operar com fluxo de potência unidirecional. Dentre esses impactos, destaca-se a elevação do nível de curto-circuito da rede, pois correntes de curto-circuito com valores elevados podem causar violação das capacidades dos equipamentos em suportar os esforços térmicos e dinâmicos e também provocar a perda da coordenação entre os dispositivos de proteção contra sobrecorrente. Neste contexto, este trabalho analisa a influência de geradores distribuídos baseados em inversores na corrente de curto-circuito trifásica em um sistema de distribuição de energia, e sobretudo, comprova que sua contribuição no valor da corrente de falta não supera o dobro de sua corrente nominal. Além disso, com base nesta comprovação, apresenta duas estratégias para inserção desse tipo de gerador nos cálculos de curto-circuito de um sistema de distribuição de energia elétrica. As duas estratégias apresentam resultados satisfatórios, utilizam conceitos básicos de circuitos elétricos, independem de dados minuciosos dos inversores e são validadas através de aplicações numéricas com resultados confrontados aos obtidos das simulações. / The installation of distributed generation in distribution and subtransmission systems has shown significant growth worldwide, driven by the benefits it can provide to electrical systems, the need to diversify the energy sources, deregulation of the electricity industry in several countries and the need to generate electricity in a sustainable manner. However, in order to evaluate if distributed generators benefit the operation of power networks, their technical impacts should be carefully studied, especially in distribution networks, which were originally designed to operate with unidirectional power flow. Among the aforementioned impacts, there is the increase of the short circuit level in the distribution network, since high short-circuit currents may exceed the capabilities of equipment to support the dynamic and thermal stresses and also cause loss of coordination between the overcurrent protection devices. Within this context, this thesis analyzes the influence of inverter based distributed generators on three-phase short circuit currents in a power distribution systems. Especially it confirms that the contribution to the fault current does not exceed twice its rated value. Furthermore, based on this issue, this work presents two strategies for the inclusion of this type of generator in short circuit calculations. Both strategies presented satisfactory results, use basic concepts of electrical circuits, they do not depend on detailed data from the inverters and the results are validated by using simulation results.

As máquinas elétricas rotativas são hoje a principal forma de transformação da energia elétrica em mecânica motriz e os motores de indução trifásicos têm grande relevância dentro do setor produtivo. A garantia de um correto funcionamento torna-se vital para eficácia e competitividade da empresa dentro do setor fabril. Assim sendo, um correto diagnóstico e classificação de falhas de funcionamento dos motores em operação pode fornecer maior segurança no processo de tomada de decisão sobre a manutenção, aumentar a produtividade e eliminar os riscos e os danos aos processos como um todo. A proposição deste trabalho baseia-se na análise das correntes de estator no domínio da frequência com sinais injetados na máquina juntamente com a modulação de alimentação para o diagnóstico do motor sem defeitos, com falhas de curtocircuito nos enrolamentos do estator e com falhas de rotor. A proposta é validada numa ampla faixa de frequências de operação bem como de regimes de conjugado de carga. São analisados os desempenhos individuais de cinco técnicas de classificadores de padrões, sendo proposta a utilização de: i) Perceptron Multicamadas, ii) Máquina de Vetores de Suporte, iii) k-Vizinhos Próximos, iv) Árvore de Decisão C 4.5 e v) Naive Bayes. Complementarmente, é desenvolvido um comparativo dos métodos de classificação de padrões para avaliar a precisão de classificação frente aos diversos níveis de severidade das falhas. Resultados experimentais com motor de 1 cv são apresentados para validar a proposta. / Rotating electric machines are today the main form of transformation of electrical energy in motor mechanics and three-phase induction motors have great relevance within the productive sector. Thus a correct diagnosis and classification of failures of the engines in operation can provide security in the decision making process on maintenance, increase productivity and eliminate risks and damages to processes as a whole. The purpose of this paper is based on the analysis of the stator currents in the frequency domain with signals injected into the machine together with the power modulation for the diagnosis of motor faultless, stator winding short-circuit faults and rotor faults. Considering also, for validation of the proposal is validated on a broad range frequency of operation as well as load torque. We analyze the individual performances of five standard classifier techniques, proposing the use of: i) Multilayers Perceptron, ii) Support Vector Machine, iii) k-Nearest Neighbor, iv) C 4.5 Decision Tree and v) Naive Bayes. Complementarily, a comparison of the methods of classification of standards is developed to evaluate the accuracy of classification against the different levels of severity of the failures. Experimental results with 735.5 w and 1.471 w engines are presented to validate the proposal.

Increased government funding and incentives in recent years has led to an increase in the number of grid-tied renewable energy sources as their economic benefits become more renowned. Unfortunately, the outputs of these renewable resources are often highly variable, resulting in undesirable voltage disruptions that are harmful to sensitive loads. In addition to the energy variability of renewable energy sources, random voltage sags, swells and disruptions are already a major issue in power systems. Recent advances in power electronic devices have provided a platform for new solutions to the voltage support problem in power systems. One promising solution is the Dynamic Voltage Regulator (DVR), a series compensating device used to protect a sensitive load that is connected downstream from voltage sag or swell. For this thesis, the design, modeling, and analysis of a DVR system were performed using PSCAD software. Results from simulation demonstrate the DVR’s effectiveness in protecting a sensitive load from load and source side voltage disturbances as well as regulate the load bus voltage to its rated value.

The purpose of the present study is to determine the thermal feasibility of an air-cooled power inverter. The inverter circuitry layout is designed in tandem with the thermal management of the devices. The cylindrical configuration of the air-cooled inverter concept accommodates a collinear axial air blower and a cylindrical capacitor with inverter cards oriented radially between them. Cooling air flows from the axial fan around the inverter cards and through the center hole of the cylindrical capacitor. The present study is a continuation of the thermal feasibility study conducted in fiscal year 2009 for the Oak Ridge National Laboratory to design a power inverter with a radial inflow cylindrical configuration. Results in the present study are obtained by modeling the inverter concept in computer simulations using the finite element method. Air flow rate, ambient air temperature, voltage, and device switching frequency are studied parametrically. Inlet air temperature was 50°C for all the results reported. Transient and steady-state simulations are based on inverter current that represents the US06 supplemental federal test procedure from the US EPA. The source of heat to the system comes from the power dissipated in the form of heat from the switches and diodes and is modeled as a function of the voltage, switching frequency, current, and device temperature. Since the device temperature is a result as well as an input variable, the steady-state and transient solution are iterative on this parameter. The results demonstrate the thermal feasibility of using air to cool an axial-flow power inverter. This axial inflow configuration decreases the pressure drop through the system by 63% over the radial inflow configuration, and the ideal blower power input for an inlet air flow rate of 540 cfm is reduced from 936 W to 312 W for the whole inverter. When the model is subject to one or multiple current cycles, the maximum device temperature does not exceed 164°F (327°F) for an inlet flow rate of 270 cfm, ambient temperature of 120°C, voltage of 650 V, and switching frequency of 20 kHz. Although the maximum temperature in one cycle is most sensitive to ambient temperature, the ambient temperature affect decays after approximately half the duration of one cycle. Of the parametric variables considered in the transient simulations, the system is most sensitive to inlet air flow rate.

It is customary to obtain ac power from batteries through a power converter, where mains ac power is not readily available. Such a power converter is also needed in several mobile/ airborne/ space applications. Till recently this application is served by a H bridge inverter followed by a low frequency transformer and a passive low pass filter. The H bridge inverter employs high frequency pulse width modulation. The transformer is made of standard silicon steel. The filter is made of L and C elements. In such a converter the magnetics account for about 30% of cost and 50% of weight. Moreover the dc input current in such converters is discontinuous, leading to poor efficiency. There is need for an input filter as well. This thesis presents the development of an inverter with high frequency (hf) link. The power converter employs a boost front end resulting in continuous input current. The H bridge inverter employs phase modulation technique with soft switching features. The boost converter and the H bridge share power devices. The isolation transformer handles high frequency ac power and is compact. It is shown that the transformer size can be reduced by more than one order of magnitude. There is a rear end cycloconverter to reconvert the high frequency ac power into 50 Hz output power. Innovative pulse sequencing in the cycloconverter ensures loss-less switching. The pulse width modulation shifts the dominant harmonic frequency to double the switching frequency. The output LC filter is light. The converter can handle bidirectional power. The controller is digital. The overall concept was demonstrated through the 500 W prototype design. The proposed topology offers small size, low losses and continous input current. The controller is digital and offers totally software based compensation and settings. It is expected that on account of the small size and cost, this topology is likely to become more popular in the near future. The applications of such power converters will bring down the size and cost of UPS, solar inverters, wind mill inverters etc.

This thesis proposes a high efficiency driving circuit for multiple light emitting diode (LED) lamps with dimming feature. The driving circuit consists of essentially a high-frequency half-bridge series resonant inverter with multiple output transformers, on which primary windings are connected in series, while secondary sides are loaded by LED lamps rated at different powers with different turn ratios. By controlling the frequency of the inverter, the resonant current as well as the lamp current can be regulated simultaneously. On the other hand, the LED lamps can be dimmed individually by the associated dimming switches with integral cycle control. The tactful circuit ensures a high circuit efficiency owing to less conducting losses and zero-voltage switching (ZVS) operation of the active power switches of the inverter and zero current switching (ZCS) operation of the dimming switches. Two prototype circuits designed for 60 W three RGB LED lamps and 50 W five white light LED lamps have been built and tested to verify the analytical predictions. Experimental results demonstrate that the driving circuit can operate the LED lamps at a high efficiency with a wide dimming range. The lamp power can be dimmed to 10% with frequency control, while whole dimming range can be achieved with integral cycle control. The circuit efficiency with integral cycle control is relatively higher than that with frequency control. The measured efficiencies for the two designed circuit are 93% and 90%, respectively, under the rated powers.

A high-frequency half-bridge series resonant inverter with multiple output transformers is developed for driving multiple cold-cathode fluorescent lamps (CCFLs) with dimming feature. The primary sides of the transformers are connected in series with the resonant inverter to have an identical current, while the secondary sides are loaded by CCFLs with galvanic isolation to each other. To ensure a high circuit efficiency, the active power switches of the inverter are designed to be switched on at zero voltage. The resonant current of the inverter can be regulated by controlling the switching frequency of the inverter, so that all CCFLs can be dimmed simultaneously. On the other hand, the primary sides of the output transformers are associated with parallel switches to dim the CCFLs individually. These dimming switches are operated at a low frequency by integral cycle control with zero current switching (ZCS) to reduce the switching losses. The resonant circuit is tactfully designed to alleviate the variation of the resonant current caused by the switching of dimming switches. A laboratory circuit is built for driving 5 CCFLs. The intended circuit performances are confirmed by test results. The variation of the resonant current is less than 10% when the dimming switches are switching, and the measured efficiency for the circuit is 96.15% under the rated powers.

Advanced pulse width modulation (PWM) techniques such as space vector PWM, active zero state PWM, discontinuous PWM, and near state PWM methods are used in three-phase AC motor drives for the purpose of obtaining low PWM current ripple, wide voltage linearity range, and reduced common mode voltage (CMV). In some applications, a filter is inserted between the inverter and the motor for the purpose of reducing the stresses in the motor. The motor current PWM ripple components, terminal voltage overshoots, shaft voltage, and bearing currents, etc. can all be reduced by means of PWM techniques and passive filters. Various PWM techniques and passive filter types exist. This thesis studies the combinations of PWM techniques and filters and evaluates the performance of the motor drive in terms of the discussed stresses in the motor. PWM techniques are reviewed, a generalized algorithm for the implementation of PWM techniques is developed, and implementation on a 4 kW rated drive is demonstrated. Filter types are studied, among them the common mode inductor and the pure sine filter (PSF) configurations are investigated in detail. Filters are designed and their laboratory performance is evaluated. In the final stage the advanced PWM techniques and filters are combined, the incompatibility problem of discontinuous PWM methods with the PSF is illustrated. A cure based on rate of change limiter is proposed and its feasibility proven in the laboratory experiments. With the use of the proposed PWM algorithm and PSF, a motor drive with ideal DC to AC conversion stage (DC to pure sine) is achieved and its performance is demonstrated in the laboratory.

In this thesis various reduced common mode voltage (RCMV) pulse width modulation (PWM) techniques and active/passive common mode voltage (CMV) reduction methods for voltage source inverter driven three-phase AC motors are theoretically and practically investigated. A novel RCMV-PWM method, the near state PWM (NSPWM) method is proposed for operation at high modulation index. At low modulation index, a modified version of an existing RCMV-PWM method, AZSPWM1, termed as MAZSPWM, is proposed to mitigate the voltage reflection problem of the method. An optimum modulation algorithm combining NSPWM and MAZSPWM with seamless transition is proposed. The proposed RCMV-PWM methods significantly reduce CMV but they suppress common mode current (CMC) partially. Utilization of a common mode inductor together with RCMV-PWM methods is effective in suppressing the CMC. In the study, in addition to the CMV characteristics, various practical performance characteristics such as voltage linearity, inverter output current ripple, inverter DC-link current ripple, and output line-to-line voltage pulse pattern are also analyzed. The study involves analysis, computer simulations, and detailed laboratory experiments.