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The work detailed in the thesis compares the performance of single-phase thyristor bridge converters under different control strategies; considering in particular the efficiency, ac side power factor and harmonic content of the current and voltage waveforms. Extensive practical investigations were performed, in which, analogue and digital control circuits were developed to provide the drive signals necessary for a converter to operate in the different control modes for: a) A series -connected fully-controlled double thyristor bridge (used mainly in traction applications) operating under sequence control and; b) A fully controlled single-bridge operating under sequence and conventional control. A novel pulse-width modulation control strategy was developed for the single-bridge converter, using gate turn-off thyristors as the switching elements, whereby output voltage control is obtained by variation of the modulation index. Turn-on and turn-off signals for the power devices were obtained using an analogue control circuit. The advantages and disadvantages of this switching strategy compared with conventional and sequence control were studied, and results clearly showed that an improved input power factor and lower supply current and load voltage harmonics were all obtained. Mathematical models for single and double bridge converters operating under sequence and conventional control were developed using tensor techniques. Using these models, computer programmes were written in Fortran 77 on the University mainframe computer, to assemble automatically and solve the network equations as the converter topology changes. In addition, analytical models were also developed on the assumption that the load current is completely smooth. However, such an assumption is not justifiable with ac-to-dc converters and consequently a novel technique was developed to include the load current ripple in calculating the supply current harmonics. The results obtained are compared with both the computed and experimental ones.

With the proliferation of residential-scale renewable energy sources and DC loads, it has become attractive to use residential DC electrical system that could offer benefits over the legacy residential AC electrical system. The Hybrid AC/DC house provides a sustainable alternative to preexisting residential electrical system by having both AC and DC buses. The DC bus facilitates the connection from DC sources to DC loads, whereas the AC bus interfaces AC sources to AC loads. The study develops the equations to calculate losses based on a model consisting of four main components: Multiple-Input Single-Output (MISO) converter, AC-DC converter, inverter, and DC-DC converter. Parameters such as AC and DC bus voltages, load consumption, and number of AC and DC branches were used to construct multiple scenarios and evaluate efficiency. Results of the study show that the Hybrid AC/DC house displays higher efficiencies than when the house has AC only sources with higher DC load consumption. Similarly, the Hybrid AC/DC house has better efficiency than when the house has DC only sources under higher AC load consumption. For the DC bus, results of the study further indicate that the higher DC voltage level yields better efficiency than those obtained from lower DC voltages.

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This dissertation is to investigate the power system service quality of a Mass Rapid Transit (MRT) system and derive the proper transformer planning to enhance the system operation efficiency. The transformer loading factor is improved by proper capacity planning by considering the power demand according to the growth of ridership. To mitigate the harmonic distortion, the installation location and capacity of harmonic filters are designed and verified by computer simulation. In this dissertation, the software programs for the AC/DC load flow study and harmonic analysis have been developed and integrated to simulate the MRT power system. To enhance the accuracy of computer simulation for the system operation with multiple trains on the main lines, the effect of voltage fluctuation to the traction effort of a train set is considered in the AC/DC load flow analysis. The mathematical model of 12-pulse uncontrolled rectifiers without interphase transformers has been derived and implemented in the programs to obtain more accurate simulation results. To achieve better cost effective capacity planning of main transformers, the unit commitment is applied to derive the optimal transformer capacity to meet the annual peak demand and provide reserve for service reliability. The power consumption of an MRT system is varied with the train operation modes and the route gradient, curvature of MRT networks. The motion equation of train sets has been applied to find the dynamic power consumption and travel distance for each time snapshot. The AC/DC load flow analysis is performed to find the annual power loading of traction substations and whole Taipei MRT network. The energy loss, investment cost of main transformers, and the system service reliability are used to define the equivalent cost of all feasible states for each dynamic programming stage. According to the computer simulation, significant cost saving has been obtained by the proposed methodology for transformer capacity planning of Taipei MRT network. Due to the dynamic load behavior of train sets, the stochastic harmonic distortion of an MRT system is simulated. The mathematical model of the 12-pulse uncontrolled rectifiers without interphase transformers is considered in the harmonic load flow analysis to solve the power demand and harmonic injection currents at traction substations for each time snapshot. According to the mean values and standard deviation of injection harmonic currents, the stochastic harmonic load flow analysis is executed to find the average value and the confidential interval of harmonic voltage distortion for all system buses. By this method, the system voltage harmonic distortion can be evaluated more accurately to provide better guidance for the strategy of harmonic mitigation. According to the results of the stochastic harmonic load flow, different strategies of harmonic distortion mitigation are investigated. Both the fixed type and switching type of passive filters are considered to be implemented. The cost function of filter investment and the harmonic distortion are used in the objective function by considering the regulation of harmonic distortion and system voltages as the constraints. By performing the nonlinear programming, the proper capacity of harmonic filters for each harmonic order and the corresponding switching time of unit commitment is determined. To further improve the power quality, the hybrid filter is also proposed for better distortion mitigation. The analysis of distortion mitigation by harmonic filters are performed to demonstrate the effectiveness of the hybrid filters to improve the power quality of MRT systems.

Les Alimentations Sans Interruption (ASI) ont pour rôle de protéger les charges sensibles. Leur utilisation nécessite l’usage de convertisseur de puissance AC/DC triphasé abaisseur et/ou élévateur de tension. Les ASI utilisent généralement une chaîne de conversion DC/DC+DC/AC ayant un rendement aux alentours de et sont souvent employées de façon continue. L’objectif de cette thèse est donc d’étudier un convertisseur DC/AC triphasé réversible en puissance susceptible de fonctionner en abaisseur et en élévateur de tension pour atteindre un rendement souhaité de 98% avec un minimum de 97,5%. L’étude s’oriente vers des architectures de convertisseurs peu conventionnelles, l’utilisation de semi-conducteurs grand gap (SiC) et de composants passifs à faible pertes. Une méthode de comparaison rapide qui est à la fois analytique et numérique est présentée pour dimensionner ces architectures en se basant sur les caractéristiques fournies par les constructeurs. La solution ‘Gradateur Onduleur Différentiel’ a été jugée comme la plus adaptée à nos besoins. Les choix techniques pour ce convertisseur sont détaillés, puis une étude de faisabilité présentée. Le convertisseur retenu est non linéaire et sa commande utilise des principes de fonctionnement atypiques, différentes stratégies de régulation sont donc présentées. Des tests sont effectués pour valider la commande mise en place et réaliser les essais fonctionnels et mesures de rendement. Enfin les résultats sont comparés aux prévisions et la solution proposée est finalement globalement comparée à la chaîne de conversion AC/DC+DC/DC classique.

No description available.

Les Alimentations Sans Interruption (ASI) ont pour rôle de protéger les charges sensibles. Leur utilisation nécessite l’usage de convertisseur de puissance AC/DC triphasé abaisseur et/ou élévateur de tension. Les ASI utilisent généralement une chaîne de conversion DC/DC+DC/AC ayant un rendement aux alentours de et sont souvent employées de façon continue. L’objectif de cette thèse est donc d’étudier un convertisseur DC/AC triphasé réversible en puissance susceptible de fonctionner en abaisseur et en élévateur de tension pour atteindre un rendement souhaité de 98% avec un minimum de 97,5%. L’étude s’oriente vers des architectures de convertisseurs peu conventionnelles, l’utilisation de semi-conducteurs grand gap (SiC) et de composants passifs à faible pertes. Une méthode de comparaison rapide qui est à la fois analytique et numérique est présentée pour dimensionner ces architectures en se basant sur les caractéristiques fournies par les constructeurs. La solution ‘Gradateur Onduleur Différentiel’ a été jugée comme la plus adaptée à nos besoins. Les choix techniques pour ce convertisseur sont détaillés, puis une étude de faisabilité présentée. Le convertisseur retenu est non linéaire et sa commande utilise des principes de fonctionnement atypiques, différentes stratégies de régulation sont donc présentées. Des tests sont effectués pour valider la commande mise en place et réaliser les essais fonctionnels et mesures de rendement. Enfin les résultats sont comparés aux prévisions et la solution proposée est finalement globalement comparée à la chaîne de conversion AC/DC+DC/DC classique. / Uninterruptible Power Supply (UPS) aim at quasi-instantaneous protection of critical loads. A DC to 3-phase AC stepup/stepdown converter is needed. For UPS, energy transfer using battery generally uses a 2-stage DC/DC+DC/AC conversion with an efficiency close to 96%. UPS are generally running permanently. The goal of this PhD is to optimize this conversion chain to aim at a target efficiency of 98% with a minimum requirement of 97%. To achieve this, our study will start with a survey of reversible architectures with both stepup and stepdown capability. Using wide bandgap semi-conductors and low-loss passive components are also part of this study. The power converter topologies are compared with a quick dimensioning method wich use both analytic analyse and simulation to realised an element selection based on characteristic given by the constructors. Eligible power converters are evaluated and compared and the “AC chopper+Inverter” architecture is found to best match our requirements. Then the technical choices of the power converter are detailed and a feasibility study is presented for the worst-case scenario. The selected power converter topology is non-linear and its control includes specific states, different strategies for the network and DC line electric parameter regulation are presented. To allow the verification of the proposed regulation, functional tests and efficiency measurement at different points are realised on the prototype. As a conclusion, the results gathered with the prototype are compared to those of a more conventional AC/DC+DC/DC power chain.

The U.S. Navy has developed in their ships, and is continually improving, electric propulsion, ship service power, and electric loads. The latest topology under design is the integrated power system (IPS). The IPS entails the all electric ship concept with electric propulsion, direct current (DC) distribution, and modular technology. In the all electric ship concept, ship propulsion and ship service loads are powered by alternating current (AC) generation. For the IPS, power electronics conversion is to be utilized to convert alternating current (AC) generation to direct current (DC) distribution. As state-of-the-art power electronics, the Navy plans to use power electronic building blocks (PEBB) technology in its IPS. A U.S. naval shipboard power system is required to be a highly reconfigurable system to enhance its survivability and reliability. Reconfiguration is a change in the shipboard power system state for various reasons such as new topology, changing missions and emergencies. It was decided to study the behavior of a PEBB-based integrated shipboard power system during reconfiguration. Since no real time operation data was available, the problem was studied through the simulation of reconfiguration scenarios on a scaled-down computer model of an IPS in MATLAB. Reconfiguration scenarios were determined and staged, and an AC/DC power system stability assessment methodology was applied by decoupling the IPS test system around an intrazonal bus. The coupled system of the test IPS, consisted of two dynamic 4160 VAC generators, two rectifiers, two DC-DC converters between the rectifiers' output looped bus and the downstream intrazonal 775V busses, inverters, buck converters, AC loads and DC loads. There was modeling of excitation perturbations which introduced errors in the assessment of the stability requiring an approximation analysis. The study found that the DC bus of interest was stable for all nine reconfiguration scenarios staged, but it found that other busses were not stable for two of the scenarios. The study further found that lower stability margins occurred at lower frequencies of about 1Hz for stable scenarios. It concluded that there were tangible benefits to advancing the shipboard power system architecture to the IPS topology because of the good stability results.

The main goal of this thesis is to improve the efficiency of power consumption for single train and propose the effects of the voltage variation to AC/DC power flow. This thesis establishes a simplified mathematic model for motor drivers with the magnetic vector control laws. Furthermore, it designs the framework of the motor drives model with the power system blockset of the MATLAB/SIMULINK. The mass rapid transit(MRT) power system framework are also introduced in the thesis. Besides the power and propelment system model are developed. Due to the differences of the load pattern for the MRT system and the other customers, the analysis can be separated into static station load and dynamic load during the train operations. Static station load is constant and easy to measure. But dynamic load leads to some extent of variation depended on the MRT network characteristics and the headway of trains. The power consumption for dynamic load is about 60-70% of the whole MRT power consumption. The whole process of starting, acceleration, coasting and stopping are realistically concerned for the simulation of MRT operation. In this thesis, the DC system is composed of a 12 pulse rectifying transformer, a conductor rail, motor-driven induction drive control, VVVF inverter, and a 3-phase motor-driven induction electric power model. The performance for single train can be obtained very efficiently with the rate curves. To perform the MRT power system simulation, an AC/DC load flow analysis has been developed with Matlab. The power system model of an simulation for Taipei MRT system has been created, the AC/DC load flow analysis is executed to analyze the effects of traction substation, voltage fluctuation, and various load under the dynamic operation for multiple trains. The efficiency of proposed methodology to solve the optimal MRT operation is verified by comparing to the results of Train Performance Simulator (TPS), which has been used by Taipei MRT project. It is suggested that the proposed rigid modeling of propulsion driving system can enhance the accuracy of system simulation and provide the tool to achieve better planing of MRT operation.