182 research outputs found

    Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

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    Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems

    Minimum Loss Conditions in a Salient-Pole Wound-Field Synchronous Machine Drive

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    The conditions for minimum losses in a salient-pole wound-field synchronous machine (WFSM) drive are studied in this paper. The drive comprises a WFSM energized by a stator inverter and excited by a dc-dc converter both tied to a DC link. The minimum-loss operation is formulated as a nonlinear constrained optimization problem with equality constraints (e.g, torque command), and inequality constraints (flux, voltage and current limits). Lagrange multipliers are applied to solve this problem analytically. At low load, the torque demand can be met using different values for two independent electric variables (e.g. stator flux and field current magnitude). These can be optimized, thereby leading to two optimal implicit conditions. At higher load, when the stator flux reaches the maximum value, the free variables reduce to one and yield a single implicit optimal condition. For these two scenarios, the paper presents analytical derivations of the optimal conditions and numerical validation using MatLab. These conditions can be used to devise a control system optimizing the drive operation

    Application of Power Electronics Converters in Smart Grids and Renewable Energy Systems

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    This book focuses on the applications of Power Electronics Converters in smart grids and renewable energy systems. The topics covered include methods to CO2 emission control, schemes for electric vehicle charging, reliable renewable energy forecasting methods, and various power electronics converters. The converters include the quasi neutral point clamped inverter, MPPT algorithms, the bidirectional DC-DC converter, and the push–pull converter with a fuzzy logic controller

    Induction Motors

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    AC motors play a major role in modern industrial applications. Squirrel-cage induction motors (SCIMs) are probably the most frequently used when compared to other AC motors because of their low cost, ruggedness, and low maintenance. The material presented in this book is organized into four sections, covering the applications and structural properties of induction motors (IMs), fault detection and diagnostics, control strategies, and the more recently developed topology based on the multiphase (more than three phases) induction motors. This material should be of specific interest to engineers and researchers who are engaged in the modeling, design, and implementation of control algorithms applied to induction motors and, more generally, to readers broadly interested in nonlinear control, health condition monitoring, and fault diagnosis

    Performance Improvement of Grid-Integrated Doubly Fed Induction Generator under Asymmetrical and Symmetrical Faults

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    The doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) suffers from voltage and frequency fluctuations due to the stochastic nature of wind speed as well as nonlinear loads. Moreover, the high penetration of wind energy into the power grid is a challenge for its smooth operation. Hence, symmetrical faults are most intense, inflicting the stator winding to low voltage, disturbing the low-voltage ride-through (LVRT) functionality of a DFIG. The vector control strategy with proportional–integral (PI) controllers was used to control rotor-side converter (RSC) and grid-side converter (GSC) parameters. During a symmetrical fault, however, a series grid-side converter (SGSC) with a shunt injection transformer on the stator side was used to keep the rotor current at an acceptable level in accordance with grid code requirements (GCRs). For the validation of results, the proposed scheme of PI + SGSC is compared with PI and a combination of PI with Dynamic Impedance Fault Current Limiter (DIFCL). The MATLAB simulation results demonstrate that the proposed scheme provides superior performance by providing 77.6% and 20.61% improved performance in rotor current compared to that of PI and PI + DIFCL control schemes for improving the LVRT performance of DFIG

    Damping subsynchronous resonance using supplementary controls around the static synchronous series compensator.

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    Masters Degree. University of KwaZulu-Natal, Durban.The demand for electric power increases rapidly with the growth in human population whereas expansion of existing power transmission infrastructure is restrained by difficulties in obtaining rights of way, resource scarcity and environmental policies inter alia. This has called for better utilization of existing transmission facilities which, for many years has been achieved through series compensation of transmission lines using conventional series capacitor banks. However, during major system disturbances, these conventional series capacitors weaken the damping of torsional oscillations in the neighboring turbine-generator shafts, which may lead to the failure and damage of the shafts concerned; a phenomenon known as subsynchronous resonance (SSR). Alternative means of series compensation using high-speed semiconductor switches has been realized following introduction of Flexible AC Transmission Systems (FACTS) in power systems. This research work focuses on damping of SSR using damping controls around the second-generation series device of the FACTS family namely the static synchronous series compensator (SSSC). The SSSC is designed to inject voltage in series with the transmission line and in quadrature with line current to emulate capacitive reactance in series with the transmission line. In this research work, a model of the SSSC is developed in Power System Computer Aided Design (PSCAD) and the IEEE First Benchmark Model (FBM) is used for SSR analysis. Initially, the resonant characteristics of the SSSC compensated transmission line is studied to determine whether this device has a potential to excite SSR on its own. The results confirm earlier work by other researchers using a detailed model of the SSSC, showing that introduction of a SSSC can indeed excite SSR, although not to the same extent as conventional series capacitors. The research work then considers the addition of supplementary damping controllers to the SSSC to add positive damping to subsynchronous oscillations caused by the SSSC itself as well as by a combination of conventional series capacitors and a SSSC in the IEEE FBM. Finally, the research work considers a more complex transmission system with an additional transmission line that incorporates conventional series capacitors. Time-domain simulation results and Fast Fourier Transform analyses show that a damping controller around the SSSC can be used to mitigate SSR either due to the SSSC itself, or due to conventional series capacitors in the same line as the SSSC or due to conventional series capacitors in an adjacent line of an interconnected transmission network

    Integration improvement of DFIG-based wind turbine into the electrical grid

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    [ENG] This doctoral thesis in electrical engineering is presented as five research works linked together by the same theme. Five articles were published in indexed journals. In this sense, each of these works forms a piece of the puzzle constructed around the subject ”wind farms integration into the electricity grid.” To better understand the articulation between these works, this thesis is structured in three parts: The first part treats the Fault Ride Through (FRT) capability of the Grid-connected DFIG-based Wind Turbine. The first proposed approach is a hybrid method combining two methods (active and passive methods): The active method aims to develop the control of DFIG. In contrast, the passive method is applied for severe voltage faults using hardware protection circuits. Otherwise, the second proposed approach is a control design implemented to the power converters using Proportional-Resonant regulators in a stationary two-phase(α−β) reference frame. The control performance is significantly validated by applying the real-time simulation for the rotor side converter and the hardware in the loop simulation technic for the experiment part of the generator’s grid side converter control. This thesis’s second part presents a new fault diagnosis and fault-tolerant control strategy for doubly fed induction generator with DC output based on predictive torque control. Generally, the current sensor failures can deteriorate the reliability and the performance of the control system and can lead to the malfunction of the predictive control strategy since the rotor-and stator flux cannot be estimated correctly. The proposed fault diagnosis can deal with all types of sensor faults. A non-linear observer adapted to the studied system to achieve smooth operation continuity when two or all the current sensors are faulty. The proposed approach’s feasibility and robustness are achieved by testing different sensor faults on the stator-and rotor-current and under different operation mode cases. The third part focuses on calculating the wind capacity credit by integrating the Moroccan project on the wind energy of 1000 MW in 2020. After introducing the Moroccan Integrated Wind Energy Project, a wind capacity credit assessment program will be implemented on Matlab software, including the complete information about” installed capacity, number of plants, failure rate, types of installed units, peak demand, etc.” This program will be used to calculate the safety rate of an electrical system as well as the capacity credit of Morocco’s electricity production network. The research provides conclusions according to comments and assessment of the impact of this electric energy integration based on wind generation. [SPA] Esta tesis doctoral en ingeniería eléctrica se presenta como cinco trabajos de investigación vinculados entre sí por un mismo tema. Se publicaron cinco artículos en revistas indexadas. En este sentido, cada uno de estos trabajos forma una pieza del rompecabezas construido en torno al tema “Integración de parques eólicos en la red eléctrica”. Para comprender mejor la articulación entre estos trabajos, esta tesis se estructura en tres partes: La primera parte trata la capacidad Fault Ride Through (FRT) de la turbina eólica basada en DFIG conectada a la red. El primer enfoque propuesto es un método híbrido que combina dos métodos (métodos activo y pasivo): El método activo tiene como objetivo desarrollar el control de DFIG. En contraste, el método pasivo se aplica para fallos severos de voltaje usando circuitos de protección de hardware. De lo contrario, el segundo enfoque propuesto es un diseño de control implementado para los convertidores de potencia utilizando reguladores de resonancia proporcional en un marco de referencia estacionario de dos fases (α−β). El rendimiento del control se valida significativamente aplicando la simulación en tiempo real para el convertidor del lado del rotor y la técnica de simulación de hardware en el bucle para la parte experimental del control del convertidor del lado de la red del generador. La segunda parte de esta tesis presenta una nueva estrategia de diagnóstico de fallos y control tolerante de fallos para un generador de inducción doblemente alimentado con salida de CC basado en control predictivo de par. Generalmente, los fallos del sensor de corriente pueden deteriorar la confiabilidad y el rendimiento del sistema de control y pueden conducir al mal funcionamiento de la estrategia de control predictivo ya que el flujo del rotor y el estator no se puede estimar correctamente. El diagnóstico de fallos propuesto puede tratar todo tipo de fallos del sensor. Un observador no lineal adaptado al sistema estudiado para lograr una continuidad de operación suave cuando dos o todos los sensores de corriente están defectuosos. La viabilidad y solidez del enfoque propuesto se logran probando diferentes fallos de sensor en la corriente del estator y del rotor y en diferentes casos de modo de operación. La tercera parte se centra en el cálculo del crédito de capacidad eólica mediante la integración del proyecto marroquí sobre la energía eólica de 1000 MW en 2020. Después de presentar el Proyecto Integrado de Energía Eólica de Marruecos, se implementará un programa de evaluación del crédito de capacidad eólica en el software Matlab, incluido la información sobre “capacidad instalada, número de plantas, tasa de fallos, tipos de unidades instaladas, pico de demanda, etc.” Este programa se utilizará para calcular la tasa de seguridad de un sistema eléctrico, así como el crédito de capacidad de la red de producción de electricidad de Marruecos. La investigación brinda conclusiones según comentarios y evaluación del impacto de esta integración de energía eléctrica basada en la generación eólicaEscuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Energías Renovables y Eficiencia Energétic

    Development of fast multi-system simulation models for permanent magnet synchronous motor and generator drive systems

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    This research project investigates the development and validation of alternative simulation models for voltage source inverter fed permanent magnet synchronous machine drive systems which can rapidly and accurately analyse and evaluate the performance of PM machine drives and associated control system designs. Traditionally simulations have been conducted using switching models and state space average value methods. The simulation of switching models is time consuming and that of state space averaging involves complex mathematical transformation to d-q axis, with additional circuitry and this limits their application in a time critical design process. Even if the complex calculations of state space are overcome, the proposed model can still achieve better results. This thesis presents the development of fast multi system simulation models for permanent magnet synchronous motor and generator drive systems. The fast simulation model: Average Voltage Estimation Model (AVEM) was developed for two-level, three phase VSI-fed PMSM drive systems and two-level three phase full-scale back-back VSI incorporated in a PMSG wind energy conversion system. The method uses the principle of control strategy and switching function to derive the average phase voltage in one switching period and then uses the average voltages to drive piecewise-linear voltage sources across the terminals of the permanent magnet synchronous machine and three phase system. A voltage source inverter loss model was also developed and incorporated into the AVEM to simulate the drive system power flow and its performance evaluated. The average voltage estimation model is also used to estimate and simulate the energy output of the variable speed PMSG wind energy conversion system. Practical implementation of this technique is achieved using a DSP based controller and validation made through comparison of the DSP AVEM energy estimation method with calculated energy. The study also presents the development of detailed VSI switching models for a variable speed PMSM and a PMSG wind energy conversion system which serve as benchmarks for the proposed AVEM models. A detailed description of both models will be presented. Since models require a control strategy: these control strategies were also developed using the carrier-based sinusoidal (SPWM) and implemented with PI regulators. In the permanent magnet synchronous generator wind energy conversion system application, the SPWM is applied to control the speed of the generator side converter to track maximum power as wind speed varies using the developed passive MPPT control technique and controls the AC load side converter to maintained constant DC link voltage. The sinusoidal PWM control provides a simplified control suitable for the variable speed PMSM drive system and the PMSG wind energy conversion system. Lastly, this thesis presents a detailed development of an experimental test rig. The test rig is developed to provide flexibility for the validation and comparison of the results of both simulation models against real practical implementations for PMSM drive system and PMSG wind energy conversions system. Several simulation case studies were performed using the PORTUNUS simulation package to validate and analyse the steady state accuracy of the proposed average voltage estimation model and control system against the switching model. Experiments were also carried out to validate the results of the simulation models. The simulation models results are presented and compared with experimental results. Suitable steady state performance analysis of two-level, three phase voltage source inverter fed permanent magnet synchronous motor and two-level three phase full scale back-back voltage source inverter with permanent magnet synchronous generator drive simulation and experimental performance are also carried out. The results show good agreement of the proposed average voltage estimation model with the switching model and experimental data, and where necessary the reasons for differences are discussed. The simulation of the AVEM is approximately 50 times faster than the switching model. The limitation of the proposed model is also discussed; mainly it cannot be used for the study and analysis of the internal dynamics of the voltage source inverter. The results from the proposed modelling method utilising the average voltage estimation confirm that this method can be used as an alternative to the detailed switching model for fast simulation and steady state analysis of PM machine drive systems given the advantages of speed, simplicity and ease of implementation. Note that the proposed model is only used for steady state performance analysis; however, in future its application can be extended to transient analysis. In addition, the model is not about maximium power point tracking techniques but it can accommodate maximium power point tracking techniques. It should also be highlighted that exactly the same digital control block is used in both the switching and AVEM models thus allowing a true comparison of controller behaviour. The model developed in this research project has application beyond PMSM drive system and PMSG wind energy conversion system. It can be applied to modelling, simulation and control of other electrical machine drives such as induction machines, switched reluctance machines and three-phase VSI-fed systems

    Modeling and Simulation of Protective Relay for Short Circuits in AC Micro-grids using Fuzzy Logic

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    The duo of high human appetite for electricity in the 21st century and high human population growth rate entail inadequacy of contemporary electric power protective systems for the emerging micro-grid. This thesis presents results of a research which seeks to propose a new model of protective device for short circuits in ac micro-grids. Response of the proposed relay is consistent with a reliable device. Consequently, a protective relay for short circuits in micro-grids is proposed
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