A control strategy for a distributed power generation microgrid application with voltage and current controlled source converter

This paper presents a pseudodroop control structure integrated within a microgrid system through distributed power generation (DPG) modules capable to function in off-grid islanded, genset-connected, and grid-connected modes of operation. System efficiency has an important role in order to harvest the maximum available renewable energy from dc or ac sources while providing power backup capability. A control strategy is proposed in off-grid islanded mode method based on the microgrid line-frequency control as agent of communication for energy control between the DPG modules. A critical case is where the ac load demand could be lower than the available power from the photovoltaic solar array, where the battery bank can be overcharged with unrecoverable damage consequences. The DPG voltage-forming module controls the battery charge algorithm with a frequency-generator function, and the DPG current source module controls its output current through a frequency-detection function. The physical installation between DPG modules is independent, since no additional communication wiring is needed between power modules, which represent another integration advantage within the microgrid-type application

Investigation to Improve the Control and Operation of a Three-phase Photovoltaic Grid-tie Inverter

Solar Energy or more precisely photovoltaic energy is one of the most promising sources of electricity for the future and it can be used as a distributed generator (DG) to play its role in ‘smart grids of the future’. Distributed PV (photovoltaic) generators can provide numerous potential benefits such as augmenting the capacity of distribution systems, deferring capital investments on distribution and transmission (T&D) systems and improving power quality and system reliability. The PV energy which possesses very special I-V and P-V characteristics has to be conditioned by a PV inverter before it can be consumed by an ac load and/or the grid. Technical improvements in maximum power point tracking (MPPT) and islanding detection are proposed for a three-phase photovoltaic grid tied inverter (GTI) keeping in mind the requirements of the international standards for connecting a DG to the utility grid. This PhD thesis will contain four major sections which are briefed below. A three phase GTI has been simulated using Matlab/Simulink to test the various control blocks and algorithms involved in the building of the power conditioning unit. A DS1104 dSpace DSP controlled, 5.625 kW three-phase GTI laboratory prototype has then been built. Various hardware components, including inverter switches, gate drivers, LCL filter, rectified dc source, boost circuit, transformer, 16A current protection circuit, additional sensing interface circuits and PWM level shifter have been designed and built within the laboratory. The software algorithm created in Simulink communicates directly with the built hardware via the graphical user interface that has been designed with dSPace Control Desk. Algorithms have been developed for the inverter in order to protect it from operating out of nominal frequency and voltage ranges. An algorithm has been developed iii to ensure the boost dc link voltage is controlled to 300V when dc voltage source varies between 150V and 265V. The Z-Source inverter (ZSI), with nine operating states that employs an extra shoot through (ST) state compared to the eight states (6 active and 2 zero states) in traditional VSI is one of the most recent boost topologies that has been proposed in the literature. A step by step design procedure of a ZSI has been developed. A topology comparison between Z-Source inverter and dc-dc boost with VSI is done using literature and simulations. Merits and demerits of the two topologies are summarised and the choice of the topology is justified. MPPT is a process by which maximum power from a PV panel or array is tracked and absorbed during a particular weather condition (insolation level and temperature). There are various MPPT techniques in the literature which are reviewed and a new MPPT approach based on the P&O (Perturb and Observe) method is proposed. The proposed technique is tested on the three phase GTI simulation, it is analysed and compared to the conventionally reviewed P&O MPPT approach. The issue of islanding of GTI’s has raised concerns of equipment and personal safety, for which reason the inverter has to detect and stop the inverter during loss of grid. Passive techniques can detect the grid failure quite well when there is a large power mismatch between the DG and the load but not when the mismatch is small. Active techniques can work well with lower levels of power mismatch but they degrade power quality by introducing disturbances into the power system. A novel wavelet based antiislanding technique is proposed and incorporated into the running hardware protection. This uses physical measurements to reduce the non-detection zone close to zero and keep the power quality of the inverter output unchanged. The developed algorithms have been validated in the laboratory prototype and yield very satisfactory performance

Protection of Electrical Power Systems with Full Penetration of Converter-Interface Generation

Mención Internacional en el título de doctorSince the advent of generation with converter-interface, mainly wind and solar photovoltaic (PV), power system operators have deal with some problems to maintain system stability and security. However, due to its low penetration in the system, it had barely any consequences and its study lack of interest. But over the years the generation scheme has changed, and converter-interface generators have been increasing their presence due to their low energy costs and policies against climate change. When the penetration rate is 100 %, protection systems have detection problems in the overcurrent scheme and pick-up problems in the distance scheme, jeopardising the safety of the electrical power system. This thesis proposes to use the Wavelet transform analysis method to solve these problems in full penetration scenarios of converter-interface generation. It can detect high and low frequency variations in voltage and current signals, and classify them in time and magnitude when they occur. In order to be able to propose a satisfactory solution, this thesis has carried out a study of the main key factors to be considered for fault detection. Analysing the differences between synchronous generators and generators with converter-interface, and the consequences of each of them for the protection systems. Describing the main converter control architectures and defining the equivalent model of converter short-circuit. Introducing the different types of faults in power systems. And describing the fundamental criteria for protection, and the most common protection schemes. The model used to obtain the results and check the feasibility of the proposal is the IEEE nine-bus system in a ring layout. It has been modelled including all power system elements (transmission lines, transformers, and loads) and both generation technologies (synchronous generators and converter-interface generators). In addition, the converter control strategy and its current limiting have also been considered. The results show a correct and immediate fault detection.Desde la aparición de los sistemas de generación de energía eléctrica con interfaz de convertidor electrónico, mayoritariamente eólica y solar fotovoltaica, los operadores de red han tenido que lidiar con los diferentes problemas que estos provocan para mantener la estabilidad y la seguridad del sistema. Aunque debido a su baja penetración en el sistema apenas tenía consecuencias y su estudio carecía de interés. Pero con el paso de los años ha ido cambiando el esquema de generación y los generadores con interfaz de convertidor electrónico han ido incrementando su presencia debido a sus bajos costes de la energía y a las políticas de lucha contra el cambio climático. Cuando se alcanzan niveles de penetración del 100 %, los sistemas de protección tienen problemas de detección en el esquema de sobrecorriente y de arranque en el esquema de distancia, poniendo en riesgo la seguridad del sistema eléctrico. Esta tesis propone utilizar el método de análisis de la transformada de Wavelet para solventar estos problemas en escenarios con máxima penetración de generación con interfaz de convertidor. El cual permite detectar variaciones de alta y baja frecuencia en las señales de tensión y de corriente, y clasificarlas tanto en tiempo como en tamaño cuando se producen. Para poder presentar una solución con garantías de ser satisfactoria, en esta tesis se ha realizado un estudio de los principales factores clave para tener en cuenta para la detección de faltas. Analizando las diferencias entre generadores síncronos y generadores con interfaz de convertidor electrónico, y qué consecuencias tiene cada uno de ellos para los sistemas de protección. Describiendo las principales arquitecturas de control de convertidores y definiendo los modelos equivalentes de cortocircuito del convertidor. Presentando los diferentes tipos de faltas en los sistemas eléctricos. Y describiendo los criterios fundamentales de las protecciones y los esquemas de protección más comunes. El modelo utilizado para la obtención de los resultados y comprobar la viabilidad de la propuesta es el sistema de nueve nudos del IEEE dispuesto en anillo. El cual ha sido modelado incluyendo todos los elementos del sistema (líneas de transmisión, transformadores y cargas) y ambas tecnologías de generación (generadores síncronos y generadores con interfaz de convertidor electrónico). Además, también se ha tenido en cuenta la estrategia de control del convertidor y su limitación de corriente. Los resultados muestran una correcta e inmediata detección de la falta.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidenta: Mónica Chinchilla Sánchez.- Secretario: Joaquín Eloy-García Carrasco.- Vocal: Roberto Lorenzo Alves Baraciart

Wavelet-fuzzy speed indirect field oriented controller for three-phase AC motor drive – Investigation and implementation

Three-phase voltage source inverter driven induction motor is used in many medium- and high-power applications. Precision in speed of the motor play vital role, i.e. popular methods of direct/indirect field-oriented control (FOC) are applied. FOC is employed with proportional–integral (P-I) or proportional–integral–derivative (P-I-D) controllers and they are not adaptive, since gains are fixed at all operating conditions. Therefore, it needs a robust speed controlling in precision for induction motor drive application. This research paper articulates a novel speed control for FOC induction motor drive based on wavelet-fuzzy logic interface system. In specific, the P-I-D controller of IFOC which is actually replaced by the wavelet-fuzzy controller. The speed feedback (error) signal is composed of multiple low and high frequency components. Further, these components are decomposed by the discrete wavelet transform and the fuzzy logic controller to generate the scaled gains for the indirect FOC induction motor. Complete model of the proposed ac motor drive is developed with numerical simulation Matlab/Simulink software and tested under different working conditions. For experimental verification, a hardware prototype was implemented and the control algorithm is framed using TMS320F2812 digital signal processor (dsp). Both simulation and hardware results presented in this paper are shown in close agreement and conformity about the suitability for industrial applications

Temperature Estimation of SiC Power Devices Using High Frequency Chirp Signals

Silicon carbide devices have become increasingly popular in electric vehicles, predominantly due to their fast-switching speeds, which allow for the construction of smaller power converters. Temperature sensitive electrical parameters (TSEPs) can be used to determine the junction temperature, just like silicon-based power switches. This paper presents a new technique to estimate the junction temperature of a single-chip silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET). During off-state operation, high-frequency chirp signals below the resonance frequency of the gate-source impedance are injected into the gate of a discrete SiC device. The gate-source voltage frequency response is captured and then processed using the fast Fourier transform. The data is then accumulated and displayed over the chirp frequency spectrum. Results show a linear relationship between the processed gate-source voltage and the junction temperature. The effectiveness of the proposed TSEPs is demonstrated in a laboratory scenario, where chirp signals are injected in a stand-alone biased discrete SiC module, and in an in-field scenario, where the TSEP concept is applied to a MOSFET operating in a DC/DC converter

Development of DC voltage control from wind turbines using proportions and integrals for three-phase grid-connected inverters

This research article presents the method to control the DC voltage of the boost converter by using a proportional-integral (PI) controller. With AC voltage from a wind turbine generator, converting to DC voltage level by rectifier, this DC voltage controlled by PI controller is to control boost converter that sends DC links to the inverter which converting alternating current voltage to direct current voltage through three-phase load and to the grid-connected system. For switching the IGBTs in the inverter, the PWM signal, on the hysteresis current control, is controlled by the signal from the detected reference voltage based on the grid-connected system and the voltage from a wind turbine generator. The tests made the comparison of results from the simulation with the MATLAB/Simulink program and result from the hardware on the prototype. The power quality results, such as harmonic, power factor, are in acceptable ranges

Real-Time Machine Learning Based Open Switch Fault Detection and Isolation for Multilevel Multiphase Drives

Due to the rapid proliferation interest of the multiphase machines and their combination with multilevel inverters technology, the demand for high reliability and resilient in the multiphase multilevel drives is increased. High reliability can be achieved by deploying systematic preventive real-time monitoring, robust control, and efficient fault diagnosis strategies. Fault diagnosis, as an indispensable methodology to preserve the seamless post-fault operation, is carried out in consecutive steps; monitoring the observable signals to generate the residuals, evaluating the observations to make a binary decision if any abnormality has occurred, and identifying the characteristics of the abnormalities to locate and isolate the failed components. It is followed by applying an appropriate reconfiguration strategy to ensure that the system can tolerate the failure. The primary focus of presented dissertation was to address employing computational and machine learning techniques to construct a proficient fault diagnosis scheme in multilevel multiphase drives. First, the data-driven nonlinear model identification/prediction methods are used to form a hybrid fault detection framework, which combines module-level and system-level methods in power converters, to enhance the performance and obtain a rapid real-time detection. Applying suggested nonlinear model predictors along with different systems (conventional two-level inverter and three-level neutral point clamped inverter) result in reducing the detection time to 1% of stator current fundamental period without deploying component-level monitoring equipment. Further, two methods using semi-supervised learning and analytical data mining concepts are presented to isolate the failed component. The semi-supervised fuzzy algorithm is engaged in building the clustering model because the deficient labeled datasets (prior knowledge of the system) leads to degraded performance in supervised clustering. Also, an analytical data mining procedure is presented based on data interpretability that yields two criteria to isolate the failure. A key part of this work also dealt with the discrimination between the post-fault characteristics, which are supposed to carry the data reflecting the fault influence, and the output responses, which are compensated by controllers under closed-loop control strategy. The performance of all designed schemes is evaluated through experiments

Engineering Education and Research Using MATLAB

MATLAB is a software package used primarily in the field of engineering for signal processing, numerical data analysis, modeling, programming, simulation, and computer graphic visualization. In the last few years, it has become widely accepted as an efficient tool, and, therefore, its use has significantly increased in scientific communities and academic institutions. This book consists of 20 chapters presenting research works using MATLAB tools. Chapters include techniques for programming and developing Graphical User Interfaces (GUIs), dynamic systems, electric machines, signal and image processing, power electronics, mixed signal circuits, genetic programming, digital watermarking, control systems, time-series regression modeling, and artificial neural networks