Dans une large variété d'applications industrielles, il existe une demande croissante pour améliorer la qualité de l'énergie fournie par les systèmes électriques. En plus de la fiabilité et de la disponibilité d'énergie électrique, la qualité de la puissance fournie devient maintenant une question importante. Parmi les causes de la pauvre qualité de puissance, les harmoniques sont considérés comme la raison qui contribue à la majorité de pannes de courant. Beaucoup d'efforts ont été développés pour résoudre le problème des perturbations harmoniques comme, par exemple, installer des dispositifs spéciaux tels que les filtres actifs. Ce travail de thèse traite le développement d’une commande directe de puissance utilisant l'approche prédictive hybride. La commande hybride considère chaque vecteur de tension du convertisseur comme une entité discrète qui sera appliquée pour commander un système linéaire continu. Un critère pour calculer le vecteur optimal de tension à appliquer sera établi à partir d’un modèle prédictif. Le vecteur optimal de tension à appliquer pour chaque période de commutation, et le correspondant temps d'application seront utilisés pour approcher la valeur réelle des variables d'état du système au point de référence désiré. Deux théories de puissance instantanées seront employées, p-q et p-q-r, pour une application de filtre active parallèle de puissance dans un système triphasé de 4 fils. Ces théories instantanées de puissance ont été développées pour être appliquées aux systèmes non équilibrés utilisant les variables de puissance pour obtenir les courants qui devraient être injectés par le filtre actif. Le filtre actif produira la puissance réactive demandée par la charge et compensera la composante d'ondulation de la puissance active de sorte que la source livre seulement la puissance active constante. / In a wide variety of industrial applications, an increasing demand exists to improve the quality of the energy provided by electrical systems. Besides the reliability and availability of electric power, the power quality is now becoming an important issue. Among the causes of the poor power quality, the harmonics are included as the reason which contributes the majority of power failures. Many efforts have been developed to solve the harmonics problem as, for instance, to install special devices such as active filters. This research work deals with the development of direct power control using the hybrid predictive control approach. The hybrid control considers each voltage vector of the converter as a discrete entity which will be applied to control a continuous linear system. One criterion to calculate the optimal voltage vector to apply will be established for the predictive control model. The optimal voltage vector to apply for each switching period, and the corresponding application time will be used to approach the actual value of the state variables of the system to the desired reference point. Two instantaneous power theories will be used, i.e. pq0 and pqr instantaneous power theory for a shunt active power filter application implemented in 3-phase 4-wire system. These instantaneous power theories have been developed to be applied to unbalanced systems using the power variables to obtain the currents that should be injected from active filters. The active filter will produce the required reactive power for the load and compensate the ripple component of active power so that the source only delivers constant active power.

Master's thesis designs a device for monitoring of electric energy consumption with ability to send measured data wirelessly using ZigBee technology. Theoretical part describes basic principles for measuring electric power and energy and also a possibility of digital measurement. Thesis provides short overview of already existing solutions for electric consumption measurement available on the market as well. Further the ZigBee standard is described together with one of its software implementations named BitCloud from Atmel Corporation. Design of the device deals with the selection of suitable integrated circuit for the consumption measurement and optimal voltage and current sensors. Then also its connection with the wireless module named ZigBee using SPI bus, power supply for the entire device and also the design of PCB. There is also a firmware implementation for the designed device based on BitCloud. Description of the firmware together with calibration process implemented is also part of the thesis. Finally, basic device testing and packet analysis of communication between designed device and ZigBee network coordinator is described.

Multifunctional voltage source converters (VSCs) are desired for shipboard power systems. The opportunity to extend the functionality of a particular VSC on demand, combined with power system reconfiguration strategies may provide desired redundancy to back up power electronic converters that might be destroyed as a result of a battle damage or material casualty. The space for power electronics may be downsized if the VSCs are capable of performing multiple functions. In addition, the flexibility of the energy management can be enhanced in shipboard power systems if a single VSC can perform multiple functions. The functionality of a VSC in many cases is restricted to a single task or set of tasks by its control architecture. Despite the great number of different control strategies suggested for VSCs, nearly all use similar methods for generation of the reference signals. These methods generally depend upon the use of filters to extract reference signals for the components that are to be injected into or drawn from the system. These methods of control are not flexible. The main objective of the dissertation is the development of a flexible reference signal generator for VSCs that allows online maximization of its possible functions. Furthermore, the switching frequency of a VSC is generally above 10 kHz for many applications, and carries a significant amount of high frequency noise. This necessitates the use of EMI filters, which carry an extra cost and increase the overall bulk of the power electronics. This may not be acceptable for shipboard power systems, where the space and weight requirements are usually stringent. Thus, in addition to investigation of various reference signal generator (RSG) strategies for VSCs, alternative solutions to attenuate EMI levels in the shipboard power system environment are explored.

This dissertation presents voltage stabilization techniques for flying capacitors used in soft-switching multilevel active power filters. The proposed active filter has proved to be a solution for power system harmonics produced by static high power converters. However, voltage unbalance of the clamping capacitors in the active filter in practical applications was observed due to its unequal parameters. Thus, the fundamentals of flying capacitors were characterized dealing with voltage balancing between flying capacitors and dc capacitors under practical operation, rather than ideal conditions. The study of voltage balancing provides the fundamental high-level solutions to flying capacitor based multilevel converter and inverter applications without additional passive balancing circuits. The use of proposed voltage balancing techniques made it possible to have a simple structure for solving the problems associated with the conventional bulky passive resistors and capacitor banks. Furthermore, the proposed control algorithms can be implemented with a real time digital signal processor. It can achieve the high performance of the active filter by compensating an adaptive gain to the controller. The effectiveness of the proposed controller was confirmed through various simulations and experiments. The focus of this study is to identify and develop voltage stabilization techniques for flying capacitors used in a proposed active filter. The voltage unbalance is investigated and characterized to provide safe operations. After having defined the problems associated with the voltage unbalance, the most important voltage stabilization techniques are proposed to solve this problem, in conjunction with an instantaneous reactive power (IRP) control of an active filter. In order to reduce the switching losses and improve the efficiency of the active filter, the proposed soft-switching techniques were evaluated through simulation and experimentation. Experimental results indicate that the proposed active filter achieved zero-voltage conditions in all of the main switches and zero-current turn-off conditions to the auxiliary switches during commutation processes. Also, various studies on soft-switching techniques, multilevel inverters, control issues and dynamics of the proposed active filter are discussed and analyzed in depth. / Ph. D.

One of the greatest technological challenges of the world today is reducing the size and weight of the existing products to make them portable. Specifically, in electric vehicles such as electric cars, UAVs and aero planes, the size of battery chargers and inverters needs to be reduced so as to make space for more parts in these vehicles. Electromagnetic Interference (EMI) filters take up a more than 80 % of these power converters, the size of these filters can be reduced by pushing the switching frequency higher. High frequency operation (> 300 kHz) leads to a size in reduction of EMI filters though it also leads to an increase in switching losses thus compromising on efficiency. Thus, soft switching becomes necessary to reduce the losses, adding more electrical components to the converter to achieve soft switching is a common method. However, it increases the physical complexity of the system. Hence, advanced control methods are adopted for today's power converters that enable soft switching for devices specifically ZVS turn-on as the turn-off losses of next generation WBG devices are negligible. Thus, the goal of this research is to discover novel switching algorithms for soft turn-on. The state-of the-art control methods namely CRM and TCM achieve soft turn-on by enabling bi-directional current such that the anti-parallel body diode starts conducting before the device is turned on. CRM and TCM result in variable switching frequency which leads to asynchronous operation in multi-phase and multi-converter systems. Hence, TCM is modified in this dissertation to achieve constant switching frequency, as the goal of this research is to be able to achieve ZVS turn-on for a three-phase converter. Further, Triangular Current Mode (TCM) to achieve soft switching and phase synchronization for three-phase two-level converters is proposed. It is shown how soft switching and sinusoidal currents can be achieved by operating the phases in a combination of discontinuous conduction mode (DCM), TCM and clamped mode. The proposed scheme can achieve soft switching ZVS turn-on for all the three phases. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kW with a density of 110 W/in3. The discussion of TCM in current literature is limited to unity power factor assumption, however this limits the algorithm's adoption in real world applications. It is shown how proposed TCM algorithm can be extended to accommodate phase shift with all the three phases operating in a combination of DCM+TCM+Clamped modes of operation. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kVA with a density of 110 W/in3. TCM operation results in 33 % higher rms current which leads to higher conduction losses, as WBG devices have lower on-resistance, these devices are the ideal candidates for TCM operation, hence to accurately obtain the device parameters, a detailed device characterization is performed. Further, proposed TCM+DCM+Clamped control algorithm is extended to three-level topologies, the control is modified to extract the advantage of reduced Common Mode Voltage (CMV) switching states of the three-level topology, the switching frequency can thus be pushed to 3 times higher as compared to state-of-the-art SVPWM control while maintaining close to 99 % efficiency. Two switching schemes are presented and both of them have a very small switching frequency variation (6%) as compared to state-of-the-art methods with >200% switching frequency variation. / Doctor of Philosophy / Power supplies are at the heart of today's advanced technological systems like aero planes, UAVs, electrical cars, uninterruptible power supplies (UPS), smart grids etc. These performance driven systems have high requirements for the power conversion stage in terms of efficiency, density and reliability. With the growing demand of reduction in size for electromechanical and electronic systems, it is highly desirable to reduce the size of the power supplies and power converters while maintaining high efficiency. High density is achieved by pushing the switching frequency higher to reduce the size of the magnetics. High switching frequency leads to higher losses if conventional hard switching methods are used, this drives the need for soft switching methods without adding to the physical complexity of the system. This dissertation proposes novel soft switching techniques to improve the performance and density of AC/DC and DC/AC converters at high switching frequency without increasing the component count. The concept and the features of this new proposed control scheme, along with the comparison of its benefits as compared to conventional control methodologies, have been presented in detail in different chapters of this dissertation.

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.

With environmental and policy pressure to move towards cleaner fuel sources, wind energy is a proven technology that can be successfully implemented at the utility-scale and provide clean energy to the grid. Wind energy consists of many distributed wind turbines that are paralleled and connected to inject power to one location on the transmission grid. There are real power losses and reactive power drops that must be taken into consideration for these projects for plant performance and compliance. The better the performance of each new and operating wind farm installed, the more efficiently the grid operates as well as the less greenhouse gases generated. This thesis will first review the creation of an Excel tool to perform a load flow study given inputs for a wind farm using Newton-Raphson algorithms. Next, the results of the load flow analysis will be compared to an actual operating wind farm located in Texas to review the accuracy of the scenarios. Finally, alternative design and operating states for the wind farm are proposed and cases are simulated to review the impact on wind farm energy generation and reactive power provided to the grid. Finally, preferred improvements for future design and operational considerations are provided along with future areas of research and development. / Master of Science / This thesis is focused on improvements for wind farm design and operation to help wind farms generate more clean power to the grid. The thesis involves the creation of an Excel tool which can be used to complete required grid studies for real and reactive power flows within the wind farm to the point of connection with the transmission system. This analysis helps inform the wind farm design and operation to be more effective and operate more efficiently. An operating wind farm in Texas is explained and depicted for an understanding of how utility-scale wind farms are set up. Additionally, a year of data from an operating wind farm is used to compare the Excel load flow tool to actual data and confirm it's accuracy. Alternate methods this plant could have been designed and operated are evaluated using the new tool and actual operating conditions from the plant for the year under analysis are performed to better understand and quantify possible improvements for wind farms. This thesis is less focused on the wind turbine generator (WTG) construction and operation of a single unit, but rather focused on the output from the WTG and the impact on an entire system containing many of these distributed generators and their operation to provide energy to the grid.

Due to the rapid growth of grid-tied solar photovoltaic (PV) systems in the generation mix, the distribution grid will face complex operational challenges. High PV penetration can create overvoltages and voltage fluctuations in the network, which are major concerns for the grid operator. Traditional voltage control devices like switched capacitor banks or line voltage regulators can alleviate slow-moving fluctuations, but these devices need to operate more frequently than usual when PV generation fluctuates due to fast cloud movements. Such frequent operations will impact the life expectancy of these voltage control devices. Advanced PV inverter functionalities enable solar PV systems to provide reliable grid support through controlled real injection and/or reactive power compensation. This dissertation proposes a voltage regulation technique to mitigate probable impacts of high PV penetrations on the distribution voltage profile using smart inverter functionalities. A droop-based reactive power compensation method with active power curtailment is proposed, which uses the local voltage regulation at the inverter end. This technique is further augmented with very short-term PV generation forecasts. A hybrid forecasting algorithm is proposed here which is based on measurement-dependent dynamic modeling of PV systems using the Kalman Filter theory. Physical modeling of the PV system is utilized by this forecasting algorithm. Because of the rise in distributed PV systems, modeling of geographic dispersion is also addressed under PV system modeling. The proposed voltage regulation method is coordinated with existing voltage regulator operations to reduce required number of tap-change operations. Control settings of the voltage regulators are adjusted to achieve minimal number of tap-change operations within a predefined time window. Finally, integration of energy storage is studied to highlight the value of the proposed voltage regulation technique vis-à-vis increased solar energy use. / Ph. D. / Rapid growth of grid-tied solar photovoltaic (PV) systems poses both opportunities and technical challenges for the electric distribution grid. Significant among them are overvoltage and voltage fluctuations in the network, which may lead to overheating of electrical devices and equipment malfunction. Due to the variable nature of solar irradiance, existing voltage control devices often need to operate more frequently than usual which can cause recurring maintenance needs for these devices. To make solar PV more grid-friendly, changes are taking place in grid codes which encourage developing advanced PV inverter functions. With these functions, a smart inverter, which possesses bidirectional communication capability, can be integrated into a smart grid environment. This work discusses how these inverters can provide active power curtailment and reactive power compensation to maintain voltages at their points of interconnection. The inherent variability and uncertainty in solar energy production can be addressed with solar forecasting. Application of PV generation forecasting as a tool to aid distribution voltage control is proposed in this dissertation. Using solar forecasting, smart inverters can contribute in relieving the stress on other voltage control devices due to PV-induced fluctuations. Integrating storage elements can also aid this voltage regulation method, as they can consume surplus PV generation when needed. This dissertation is designed to provide a systematic approach to manage the overvoltage and voltage fluctuations on a real-time basis for a high PV penetration scenario. Proposed methodology combines smart inverter functionalities with solar forecasting and develops an application which can be realized to ensure seamless PV integration in a growing landscape of renewables.

Este trabalho apresenta um método utilizando redes neurais artificiais para a determinação das amplitudes e fases dos componentes harmônicos presentes na corrente de carga monofásica. O número de harmônicos identificados é previamente selecionado. Os hamônicos identificados estão presentes na corrente de cargas não-lineares de um sistema de iluminação onde é considerada a variação no tempo das características da forma de onda desta corrente. Os harmônicos presentes no sistema degradam a qualidade de energia, sendo assim é apresentado um breve estudo sobre este tema e métodos para atenuar a distorção harmônica no sistema. Dentre estes métodos é dado ênfase na aplicação de filtros ativos de potência em paralelo com carga não-linear. O trabalho também apresenta um estudo sobre os mais comumente métodos utilizados na identificação harmônica. Dentre eles está o método baseado em redes neurais artificiais. Este método é validado com base nos dados levantados por meio de simulação e de forma experimental. / In this thesis artificial neural networks are employed in a novel approach to identifying harmonic components of the single-phase nonlinear load current, whose amplitudes and phase angles are subject to unpredictable changes in steady-state. An identified harmonics number is previously selected. These harmonics are present in the non-linear loads current of electrical illumination system. The harmonics in the power system degrade the power quality, then is exhibited a concise study dealing with power quality problems and methods to mitigate the harmonic distortion in the power system. Among these methods emphasis is given in the application of pure active power filters in parallel with the non-linear load. The thesis also shows a study about the more commonly methods used in the harmonic detection. Among them is the method based on artificial neural networks. Simulation and experimental results are presented to validate the proposed approach.

Este trabalho apresenta o estudo, análise e a implementação de três topologias de condicionadores ativos de energia elétrica, utilizados para a melhoria da qualidade da energia em sistemas elétricos trifásicos a quatro fios. Estes condicionadores de qualidade de energia podem trabalhar tanto como um condicionador unificado de qualidade de energia (UPQC), bem como uma fonte de alimentação ininterrupta (UPS), permitindo: (i) a supressão das correntes harmônicas da carga; (ii) a compensação de energia reativa da carga; (iii) compensação dos desequilíbrios das correntes de carga; (iv) a compensação de desequilíbrios de tensão da rede; (v) supressão das tensões harmônicas da rede elétrica; (vi) a regulação das tensões de saída (tensões de carga); e (vii) fornecimento de energia ininterrupta para as cargas críticas (sistema UPS). Dentre as três topologias de UPQC/UPS estudadas, uma delas é proposta neste trabalho com o intuito de reduzir a tensão no barramento CC. Além disso, todas as topologias em estudo são constituídas por dois conversores PWM, nos quais é adotada uma estratégia de controle dual. Desse modo, o conversor colocado em paralelo com a carga, funciona como uma fonte de tensão senoidal, enquanto que o conversor colocado em série entre a rede elétrica e a carga, é controlado para operar como uma fonte de corrente senoidal. Tanto os controladores de tensão, quanto os de corrente são implementados no referencial síncrono dq0. Além disso, a técnica de modulação vetorial espacial tridimensional (3-D-SVM) é empregada nos conversores. Testes experimentais são apresentados para validar o desenvolvimento teórico e verificar o bom desempenho estático e dinâmico dos condicionadores ativos de energia elétrica, operando como UPQC, bem como sistema UPS. / This work presents the study, analysis and implementation of three topologies of active power conditioners, which are used to improve the power quality in three-phase four-wire systems. These power quality conditioner can work as unified power quality conditioner (UPQC), as well as an uninterruptible power supply (UPS) system allowing: (i) suppression of load harmonic currents; (ii) compensation of load reactive power; (iii) load unbalances compensation; (iv) utility voltage unbalances compensation; (v) utility voltage harmonics suppression; (vi) regulation of the output voltages (load voltages); and (vii) uninterruptible power for critical loads when working as UPS system. Among the three topologies of UPQC/UPS studied, one of them is proposed in this work in order to reduce the DC-bus voltage. Besides, all the topologies are comprised of two PWM converters, where a dual control strategy is adopted. The first converter, which is placed in parallel with the load, operates as a sinusoidal voltage source, while the second, which is placed in series between the utility grid and the load, is controlled to operate as a sinusoidal current source. Both the voltage and current controllers are implemented into the synchronous rotating reference frame (dq0-axes). In addition, the series and parallel converters use the three-dimensional space vector modulation (3-D-SVM) technique. The experimental tests are presented to validate the theoretical development and to verify the effective static and dynamic performance of the proposed active power conditioners, operating as UPQC and UPS.