Método generalizado da oscilação forçada para sintonia de controladores proporcional-integral-derivativo e proporcional-múltiplos-ressonantes

Este trabalho propõe o método generalizado da oscilação forçada para sintonia de controladores proporcional-integral-derivativo, proporcional-ressonante e proporcionalmúltiplos- ressonantes, utilizando a filosofia de projeto do método da oscilação forçada de Ziegler-Nichols. A metodologia é aplicada a processos causais, lineares e invariantes no tempo cuja resposta em frequência não necessariamente cruza a linha de 180 de fase. Esse método é baseado no experimento do relé com fase ajustável, que possibilita a identificação do ponto mais apropriado da resposta em frequência de cada classe de processos em um único tipo de experimento. A etapa de projeto é realizada por meio dos conjuntos de fórmulas de sintonia, os quais foram desenvolvidos para cada classe de processos e para cada topologia de controle, considerando o ponto da resposta em frequência identificado e a obtenção de adequadas margens de estabilidade. A aplicação do método proposto, o qual inclui o experimento de identificação e os conjuntos de fórmulas de sintonia desenvolvidos, é realizada por meio de exemplos numéricos e também através da implementação prática dos controladores em processos reais, mostrando sua ampla aplicabilidade.This work proposes the generalized forced oscillation method for tuning proportionalintegral- derivative, proportional-resonant, and proportional-multi-resonant controllers using the Ziegler-Nichols’s forced oscillation method philosophy. The methodology applies to causal linear time-invariant plants whose frequency response does not necessarily cross the 180 phase line. This method is based on the relay with adjustable phase experiment, which enables the identification of the most appropriate point of the frequency response for each class of plants in a single type of experiment. The design procedure is performed through sets of tuning formulas that were developed for each class of plants and each control topology, considering the identified frequency response point and aiming at obtaining appropriate stability margins. The application of the proposed methodology, which includes the identification experiment and the developed tuning formulas, is performed by means of numerical examples and implementation of the designed controllers into actual physical plants, showing its wide applicability

Optimal Hierarchical Control for Smart Grid Inverters Using Stability Margin Evaluating Transient Voltage for Photovoltaic System

This research proposed an optimal control approach for a smart grid electrical system with photovoltaic generation, where the control variables are voltage and frequency, which aims to improve the performance through addressing the need for a balance between the minimization of error and the operational cost. The proposed control scheme incorporates the latest advancements in heuristics and hierarchical control strategies to provide an efficient and effective solution for the smart grid electrical system control. Implementing the optimal control scheme in a smart power grid is expected to bring significant benefits, such as the reduced impact of renewable energy sources, improved stability, reliability and efficiency of the power grid, and enhanced overall performance. The optimal coefficient values are found by minimizing the cost functions, which leads to a more efficient system performance. The voltage output response of the system in a steady state is over-damped, with no overshoot, but with a 5% oscillation around the target voltage level that remains consistent. Despite the complexity of nonlinear elements’ behavior and multiple system interactions, the response time is fast and the settling time is less than 0.4 s. This means that even with an increase in load, the system output still meets the power and voltage requirements of the system, ensuring efficient and effective performance of the smart grid electrical systems

Contributions to cascade linear control strategies applied to grid-connected Voltage-Source Converters

El trabajo desarrollado en esta Tesis se centra en optimizar el comportamiento de Voltage-Source Converters (VSCs) cuando son utilizados como interfaz con la red eléctrica, tanto para absorber como para entregar energía de la red con la mejor calidad posible y cumpliendo con los estándares. Para tal fin, esta Tesis se centra en el control de sistemas lineales conectados en cascada aplicados al control de VSCs conectados en paralelo con la red eléctrica a través de un filtro L, especialmente en conexiones con redes débiles y en dos líneas de trabajo: (i) seguimiento de armónicos de las corrientes de red y rechazo de armónicos de las tensiones de red, y (ii) control de la tensión del PCC en caso de desequilibrio. Para ello, esta Tesis realiza contribuciones en el área del control de corriente y control de la tensión del PCC. De entre las técnicas existentes para implementar el control de corriente para compensación armónica, dos de las más utilizadas son el control resonante y el control repetitivo, tanto en ejes de referencia estacionarios como síncronos. Se ha realizado un exhaustivo estudio de diferentes estructuras para implementar tales controles, mostrando su algoritmo adaptativo en frecuencia para cada una de ellas y analizando su carga computacional. Además, se han facilitado directrices básicas para su programación en un DSP. Se ha analizado también el esquema de control de corriente para establecer una comparación entre las diferentes estructuras. Después de estudiar en profundidad el control de corriente de un VSC conectado a la red eléctrica, el segundo control a analizar es el control de tensión del PCC. La presencia de una tensión desequilibrada en el PCC da lugar a la aparición de una componente de corriente de secuencia negativa, que deteriora el comportamiento del sistema de control cuando se emplean las técnicas de control convencionales. Los STATCOMs son bien conocidos por ser una aplicación de potencia capaz de llevar a cabo la regulación de la tensión en el PCC en líneas de distribución que pueden ser susceptibles de sufrir perturbaciones. Esta Tesis propone el uso de un controlador de tensión en ejes de referencia síncronos para compensar una tensión desequilibrada a través de un STATCOM, permitiendo controlar independientemente tanto la secuencia positiva como la secuencia negativa. Además, este controlador incluye aspectos como un mecanismo de antiwindup y droop control para mejorar su comportamiento. Se han realizado varias pruebas experimentales para analizar las características de los controladores de corriente abordados en esta Tesis. Todas ellas han sido realizadas bajo las mismas condiciones de potencia, tensión y corriente, de modo que se pueden extraer resultados comparativos. Estas pruebas pretenden caracterizar la respuesta transitoria, la respuesta en régimen permanente, el comportamiento frente a saltos de frecuencia y la carga computacional de los controladores de corriente estudiados

Proportional-resonant current controller with orthogonal decoupling on the aß-reference frame

The increasing penetration of grid-connected RES systems, advanced control algorithms have been developed to operate under grid faults and fulfill strict requirements of the grid codes. In order to overcome this, the current controller performance is critical considering it as the inner control loop of any grid-connected RES system. Based on the resonant control concept, this paper presents a modified structure for this controller which results advantageous when implemented on RES systems, as it permits better performance during the dynamic state of the controller. This paper also deals with the analysis of the decoupling terms in the aß reference frame, as well as the capability to generate a decoupled control of the positive and the negative sequence. The proposed controller will be analyzed, discussed and finally validated by means of simulation analysis.Peer ReviewedPostprint (author's final draft

Design Optimization of Inductive Power Transfer Systems for Contactless Electric Vehicle Charging Applications

Contactless Electric Vehicle (EV) charging based on magnetic resonant induction is an emerging technology that can revolutionize the future of the EV industry and transportation systems by enabling an automated and convenient charging process. However, in order to make this technology an acceptable alternative for conventional plug-in charging systems it needs to be optimized for different design measures. Specifically, the efficiency of an inductive EV charging system is of a great importance and should be comparable to the efficiency of conventional plug-in EV chargers. The aim of this study is to develop solutions that contribute to the design enhancement of inductive EV charging systems. Specifically, generalized physics-based design optimization methods that address the trade-off problem between several key objectives including efficiency, power density, misalignment tolerance, and cost efficiency considering critical constraints are developed. Using the developed design methodology, a 3.7kW inductive charging system with square magnetic structures is investigated as a case study and a prototype is built to validate the optimization results. The developed prototype achieves 93.65% efficiency (DC-to-DC) and a power density of 1.65kW/dm3. Also, self-tuning power transfer control methods with resonance frequency tracking capability and bidirectional power transfer control are presented. The proposed control methods enhance the efficiency of power converters and reduce the Electromagnetic Interference (EMI) by enabling soft-switching operations. Several simplified digital controllers are developed and experimentally implemented. The controllers are implemented without the use of DSP/FPGA solutions. Experimental tests show that of the developed simplified controllers can effectively regulate the power transfer around the desired value. Moreover, the experiments show that compared to conventional converters, the developed converters can achieve 4% higher efficiency at low power levels. Moreover, enhanced matrix converter topologies that can achieve bidirectional power transfer and high efficiency with a reduced number of switching elements are introduced. The self-tuning controllers are utilized to design and develop control schemes for bidirectional power transfer regulation. The simulation analyses and experimental results show that the developed matrix converters can effectively establish bidirectional power transfer at the desired power levels with soft-switching operations and resonance frequency tracking capability. Specifically, a direct three-phase AC-AC matrix converter with a reduced number of switches (only seven) is developed and built. It is shown that the developed converters can achieve efficiencies as high as 98.54% at high power levels and outperform conventional two-stage converters

Culture, Efficacy, and Outcome Expectancy in Teacher Preparation;How Do the Beliefs of Pre-Service Interns, Mentor Teachers, University Supervisors and Teacher Educators Compare?

Researchers agree that teachers\u27 attitudes and efficacy beliefs play a significant role in student achievement (Armor et al., 1976 Hoy & Spero, 2005 Szabo & Mokhtari, 2004 Woolfolk & Hoy, 1990). Teachers with high self-efficacy: 1) believe they can positively influence students\u27 learning and achievement despite environmental conditions (Armor et al., 1976 Ashton & Webb, 1986 Gibson & Dembo, 1984) and 2) assume accountability for student learning (Gibson & Dembo, 1984 Ross, 1998 Siwatu, 2007). On the contrary, teachers with low teacher efficacy have minimal expectations for and fewer interactions with minority students. They are also more likely to feel teacher burnout and abandon the profession (Betoret, 2006 Friedman, 2004 Guerra, Attar, & Weissberg, 1997). Various studies have confirmed that even after successfully completing multicultural courses and field experiences, interns\u27 negative beliefs and low outcome expectancies for minority students remained (Garmon, 1996, 2004 Easter, Schultz, Neyhart & Reck, 1999). Although little is known about how teaching efficacy develops, it is possible that programs incorporating efficacy-building opportunities assist to create and maintain a pool of quality teachers in culturally diverse schools (Clark & Wegener, 2009 Garcia, 2004 Milner, 2005 Santoro & Allard, 2005 Tucker et al., 2005 Siwatu, 2007 Swearingen, 2009). The purpose of this study will be to examine patterns in culturally responsive teaching self efficacy and outcome expectancies between interns, mentor teachers, university supervisors, and teacher educators in an urban teacher education progra

Culture, Efficacy, and Outcome Expectancy in Teacher Preparation;How Do the Beliefs of Pre-Service Interns, Mentor Teachers, University Supervisors and Teacher Educators Compare?

Researchers agree that teachers\u27 attitudes and efficacy beliefs play a significant role in student achievement (Armor et al., 1976 Hoy & Spero, 2005 Szabo & Mokhtari, 2004 Woolfolk & Hoy, 1990). Teachers with high self-efficacy: 1) believe they can positively influence students\u27 learning and achievement despite environmental conditions (Armor et al., 1976 Ashton & Webb, 1986 Gibson & Dembo, 1984) and 2) assume accountability for student learning (Gibson & Dembo, 1984 Ross, 1998 Siwatu, 2007). On the contrary, teachers with low teacher efficacy have minimal expectations for and fewer interactions with minority students. They are also more likely to feel teacher burnout and abandon the profession (Betoret, 2006 Friedman, 2004 Guerra, Attar, & Weissberg, 1997). Various studies have confirmed that even after successfully completing multicultural courses and field experiences, interns\u27 negative beliefs and low outcome expectancies for minority students remained (Garmon, 1996, 2004 Easter, Schultz, Neyhart & Reck, 1999). Although little is known about how teaching efficacy develops, it is possible that programs incorporating efficacy-building opportunities assist to create and maintain a pool of quality teachers in culturally diverse schools (Clark & Wegener, 2009 Garcia, 2004 Milner, 2005 Santoro & Allard, 2005 Tucker et al., 2005 Siwatu, 2007 Swearingen, 2009). The purpose of this study will be to examine patterns in culturally responsive teaching self efficacy and outcome expectancies between interns, mentor teachers, university supervisors, and teacher educators in an urban teacher education progra