Control digital vectorial con sliding en fuente de corriente para convertidores CC/CA trifásicos conectados a red

La energía ha sido desde la antigüedad un factor impulsor del desarrollo de la sociedad, pero no siempre su uso ha respetado la preservación de la naturaleza y el medio ambiente. En ese sentido, las fuentes tradicionales de generación de energía, como los hidrocarburos y la energía nuclear, son altamente contaminantes, por lo que se plantea una contradicción al desearse un desarrollo sostenible que no comprometa el bienestar de las futuras generaciones. la utilización de las energías solar y eólica como fuentes de energías primarias está limitada actualmente debido a la competencia de las grandes transnacionales del petróleo que ajustan los precios para entorpecer su desarrollo. En los últimos años se ha notado un creciente interés por parte de los gobiernos europeos, que han subvencionado la investigación y desarrollo de nuevos centros de cogeneración solar y eólica. las fuentes de energías alternativas producen corriente continua y las cargas industriales consumen corriente alterna, por lo que es necesaria una etapa intermedia de conversión. A esta etapa se le denomina conversión continua-alterna y a los equipos que la realizan convertidores CC/CA o inversores. Las técnicas de modulación del ancho del pulso (PWM, del inglés Pulse Width Modulation) han sido objeto de un amplio estudio durante las últimas décadas [BRO88], [DIX88], [HOL92], [MOH95], [NOV96]. Una gran variedad de métodos, diferentes en su concepto y funcionamiento, han sido ampliamente desarrollados y descritos en la literatura. Su implementación en el control de convertidores CC/CA dependerá, por ejemplo, de la aplicación, del nivel de potencia, y de los dispositivos semiconductores empleados en el convertidor de potencia.Para solventar la desventaja del control PWM clásico se utiliza el control Sliding en fuente de corriente, decidiendo el estado de los polos en tiempo real en función de las medidas de corriente. Este tipo de control tiene la virtud de adaptarse a los cambios que se produzcan en la carga, por lo que tendrá una respuesta dinámica muy rápida. En cambio, tiene la desventaja de la gran capacidad de cálculo que necesita, por lo que requiere el empleo de Procesadores Digitales de Señales (DSP del inglés Digital Signal Processor. La aplicación del vector de Park a sistemas trifásicos constituye una poderosa herramienta para el análisis y control de los convertidores CC/CA trifásicos alimentando diferentes tipos de cargas (motor asincrono trifásico, UPS, conexión a red, etc.) haciendo posible el desacople de las ecuaciones diferenciales que rigen el comportamiento de los sistemas en ejes rotatorios independientes, sin perder de vista el significado físico que las magnitudes del vector de Park representan La tesis se divide la siguiente manera: el capitulo 1 es la introducción,el segundo capítulo brinda una visión general de los fundamentos teóricos del funcionamiento de los convertidores de potencia.Capítulo 3 presenta un resumen de las características del vector de Park y la posibilidad de su empleo en sistemas trifásicos equilibrados, el 4 se presenta un nuevo observador de estado y se compara su comportamiento con el observador de estado anterior, propuesto por Domínguez. Por medio de la simulación se traza su función de transferencia de tensión y se calculan las distorsiones armónicas de la tensión y la frecuencia observadas.En el 5 se presentan las estrategias de control sliding vectorial en fuente de corriente propuestas, tanto para el control en tres como en cinco niveles, por medio de la aplicación del vector de Park,.En el capítulo 6, se lleva a cabo el dimensionado del equipo conectado a red, calculándose las constantes del regulador de la tensión de continua y garantizando la entrega de la máxima potencia a la red.En el capítulo 7 se hace un descripción resumida de las PLD's. Por último, las conclusiones de la tesis se encuentran en el capítulo 8.Universidad de ValladolidPrograma de doctorado en Tecnología Electrónica y Teoría de la Seña

Modeling and design of the vector control for a three-phase single-stage grid-connected PV system with LVRT capability according to the spanish grid code

This article deals with the vector control in dq axes of a three-phase grid-connected photovoltaic system with single-stage topology and low-voltage-ride-through capability. The photovoltaic generator is built using an array of several series-parallel Suntech PV modules and is modeled as a Lookup Table (two-dimensional; 2-D). The requirements adopted when grid voltage sags occur are based in both the IEC 61400-21 European normative and the allowed amount of reactive power to be delivered according to the Spanish grid code, which avoids the disconnection of the inverter under grid faults by a limitation in the magnitude of the three-phase output inverter currents. For this, the calculation of the positive- and negative-sequences of the grid voltages is made and a conventional three-phase Phase-Locked Loop is used for the inverter-grid synchronization, allowing the control of the active and reactive powers solely with the dq components of the inverter currents. A detailed enhanced flowchart of the control algorithm with low-voltage-ride-through capability is presented and several simulations and experiments using Matlab/SIMULINK and the Controller Hardware-in-the-Loop simulation technique, respectively, are run for several types of one- and three-phase voltage sags in order to validate its behavior.This work was supported by: the project "Nuevas topologias para convertidores en MT para grandes Instalaciones Fotovoltaicas" from the Spanish Government (Ref. TEC2016-80136-P) (A. B. Rey-Boue); the European Community's Horizon 2020 Program (H2020/2014-2020) in project "ERIGrid" (Grant Agreement No. 654113) under the Trans-national Access (TA) User Project: 04.003-2018

Frequency-adaptive control of a three-phase single-stage grid-connected photovoltaic system under grid voltage sags

The low-voltage ride-through service is carried out in this paper according to the voltage profile described by the IEC 61400-21 European normative when short-duration voltage sags happen, and some instantaneous reactive power is delivered to the grid in accordance with the Spanish grid code; the mandatory limitation of the amplitude of the three-phase inverter currents to its nominal value is carried out with a novel control strategy, in which a certain amount of instantaneous constant active power can also be delivered to the grid when small or moderate voltage sags happen. A Multiple second order generalized integrator frequency-locked loop synchronization algorithm is employed in order to estimate the system frequency without harmonic distortions, as well as to output the positive- and the negative- sequence of the {\alpha}\b{eta} quantities of the three-phase grid voltages when balanced and unbalanced voltage sags happen in a frequency-adaptive scheme. The current control is carried out in the stationary reference frame, which guarantees the cancellation of the harmonic distortions in the utility grid currents using a Harmonic compensation structure, and the implementation of a constant active power control in order to protect the DC link capacitor from thermal stresses avoiding the appearance of large harmonic distortions at twice the fundamental frequency in the DC link voltage. A case study of a three-phase single-stage grid-connected PV system with a maximum apparent power about 500 kVA is tested with several simulations using MATLAB/SIMULINK firstly, and secondly, with some experiments using the Controller hardware-in-the-loop (CHIL) simulation technique for several types of voltage sags in order to do the final validation of the control algorithms

Editorial: Grid Connection of Converters in Renewable Applications

Energy generated from renewable sources is fed into the grid by means of electronic power converters. These can be supervised at system (grid) level to coordinate all productions points together with storages and loads. Regulations impose power supply quality requirements regarding harmonics, grid fault response and low voltage ride through (LVRT). The progress of distributed generation presents challenges to converters such as island mode operation, voltage and frequency regulation, simulation, etc. New collaborative solutions for “more smart” microgrids must be included to improve power quality, reliability, service quality and duty. Wind turbines employing double-fed induction generators (DFIG) use two converters, one for the rotor side and one for the generator side. To improve the performance during severe grid failures, in Okedu and Barghash the advantages of using alternative configurations to the two-level converter, such as the parallel interleaved 2-level inverter, and the 3-level inverter, have been investigated. It has also been investigated to replace the classical dq-PLL with a new PLL, and to include a series dynamic braking resistor (SDBR) between the converters and the three-phase connections. Wind turbines must meet strict requirements, in terms of their behavior, in the event of grid failures, which are regulated by the LVRT regulations in each country. These regulations indicate, by means of voltage and time graphs, how long the wind turbines must remain connected depending on the depth of the faults. In addition, the limits of active and reactive power that can be exchanged during faults are established. The aim is to avoid cascading disconnections of wind turbines that would compromise the stability of the grid. In Okedu and Barghash, the effect of various elements in improving the behaviour of a DFIG against grid faults has been investigated. The first of these elements is the parameters of the IGBTs, concluding that the on-resistance has the greatest influence. The second is the use of a new PLL, and the third is the use of a SDBR during a grid failure. It was found that all of them could improve the performance of the generator in the event of a grid failure. When a wind turbine uses a permanent magnet synchronous generator (PMSG), 100% of the energy generated passes through both converters. In Okedu and Barghash, the control systems of the generator-side and grid-side converters have been considered; several scenarios regarding the turn on resistance of the IGBTs have been considered, and their behaviour during grid faults has been analysed. Generator performance has also been studied with and without the use of a DC-DC converter for overvoltage protection. The main generators used in wind turbines are DFIG and PMSG. In Okedu et al., a comparison of the behaviour of both wind turbines against grid faults has been carried out in various scenarios with different values of generator parameters. The number of converters, associated with renewable generation, connected to the grid has increased significantly lately. This can affect the dynamic response, especially during disturbances, but it can also provide new grid support functionalities if information on the oscillation characteristics is available. Through the use of artificial intelligence, in Baltas et al. the abilities to predict and damp electromechanical oscillations have been improved. With the constant increase in the number of wind turbines connected to the grid, it is very important to have the ability to maintain grid frequency control. In Okedu and Barghash, a work has been presented to stabilise the wind farm during periods of wind speed change by using capacitors connected via a DC-DC converter and a grid-connected DC-AC converter. It was concluded that higher values of the DC-DC converter time constant lead to better performances during load transients. A system including two steam turbines and two squirrel cage induction generators was used in the experiments. Microgrids bring power generation closer to the places of consumption to reduce the saturation of distribution lines. They consist of renewable generation, energy storage and fossil fuel generation. They have three levels of control, where the primary level is the closest to the converters, and the tertiary level, the most external and slowest, performs general monitoring functions. The paper (Buraimoh et al.) focuses on the secondary control functions related to grid failure performance. It proposes a distributed control between inverters and is based on fast detection techniques (fast Delayed Signal Cancellation, DSC), with the objective of a fast control of active and reactive power. A robust transition method between fault mode and normal mode is proposed. Accurate coordination and power sharing between distributed energy resources is achieved. Some energy conversion systems are so complex that they are very difficult to build and test in the laboratory. These include the study of high voltage direct current (HVDC) transmission when several modular multilevel converters (MMC) are involved together with DC grid failure protection elements. In Wang et al., a system including a simulated part (two digitally simulated MMC) and a physical part (two MMC) has been experimented with. The coupling between the two parts has been carried out by means of A/D and D/A converters and power amplifiers

Improved control of grid-connected DFIG-based wind turbine using proportional-resonant regulators during unbalanced grid

The quality of power and current control are the greatest challenges of grid-connected wind farms during abnormal conditions. The negative- and positive-sequence components of the grid currents may be injected into a wind generation system during grid faults, which can affect the power stability and damage the wind system. The proposed work assures a low-voltage ride through capability of doubly-fed induction generator- based wind turbines under the grid voltage sag. A new technique to protect the wind system and to recompense the reactive power during failures of the utility grid according to the Spanish grid code is proposed. The control design is implemented to the power converters, and the grid current regulation is developed by using proportional-resonant regulators in a stationary two-phase (alpha beta) 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 technique for the experiment of the generator's grid-side converter control.This work was supported by: the project "Nuevas topologias para convertidores en MT para grandes Instalaciones Fotovoltaicas" from the Spanish Government (Ref. TEC2016-80136-P) (from A.B.R.); the European Community's Horizon 2020 Program (H2020/2014-2020) in project "ERIGrid" (grant ggreement No. 654113) under the Trans-national Access (TA) User Project (Ref. 04.003-2018); and the Erasmus + KA107 mobility program 2018/2019 between Europe and Morocco, Universidad Politecnica de Cartagena (UPCT) & Sidi Mohamen Ben Abdellah University (USMBA)-Fez (from Y.E.K.)

Enhanced controller for grid-connected modular multilevel converters in distorted utility grids

This paper is about the control of Modular multilevel converters, an innovative technology in the design of converters, which is beginning to be included in real installations. Papers about this topic include simulation models, circulating current reduction, voltage modulators, capacitor voltage balancing and control issues. The scheme for current source regulation used in this article includes all control loops, which are, from the outermost to innermost, DC bus voltage regulator, current regulator, voltage modulator, capacitor voltage balancing, and a PLL for the synchronization to the grid. Disposition-sinusoidal pulse width modulation is used as the voltage modulator, and an enhanced control strategy in the stationary reference frame for 3-phase MMCs is used for the inner current control loops. Very detailed simulations of the complete control system have been performed for both the enhanced control strategy in the stationary reference frame, and the well-known control in the synchronous reference frame, as well as some experiments using the hardware-in-the-loop simulation technique. The validation of these control strategies is made by a comparison of the capability of each one to compensate the harmonic distortions of the utility grid according to the grid code. The correct operation has been tested in the case of a strong/weak grid, unbalances and grid failures.This work has been partially supported by a grant from the Spanish Government as a part of 673 Project Ref. TEC2016-80136-P, entitled “Nuevas topologías para convertidores en MT para grandes 674 Instalaciones Fotovoltaicas” (A. B. Rey-Boué

Real time test benchmark design for photovoltaic grid connected control systems

This paper presents a dual digital signal processor (DSP) hardware architecture for a grid-connected photovoltaic interface test benchmark, based on a cascade DC/DC converter and DC/AC inverter, with coordinated control algorithms. The control hardware has been designed to test distributed generation (DG) interfaces to be integrated in a hierarchical structure of computational agents, to apply distributed control techniques to the power system management. The proposed dual DSP architecture enables the programming of the control software for the DC/DC converter and the DC/AC inverter in the same processor, to keep the other one for additional operations that are required when there is a high degree of interaction between the DG unit and the rest of the electrical grid components. The hardware architecture has been tested in several real situations such as power factor correction and anti-islanding protection

Sistema de ayuda al telediagnóstico de enfermedades cardiovasculares basado en el análisis de fonocardiogramas

Gracias a los recientes avances producidos en electrónica y telecomunicaciones, la fonocardiografía se presenta actualmente, tras muchos años en el olvido, como un método sencillo, rápido, barato y no invasivo capaz de obtener un diagnóstico remoto y objetivo del estado funcional del corazón mediante sistemas electrónicos que procesen los sonidos cardíacos de forma adecuada. En este trabajo se presenta un sistema de ayuda al telediagnóstico de patologías cardiovasculares a partir del registro y procesamiento de sonidos cardíacos. El sistema es capaz de detectar los eventos que componen el ciclo cardíaco (sonidos y soplos), y transmitir a distancia tanto el informe del análisis realizado como las señales registradas íntegras, para obtener de forma remota el diagnóstico del médico especialista. La transmisión de las señales se realiza comprimiéndolas con un algoritmo especialmente desarrollado para señales fonocardiográficas, que produce tasas de compresión superiores a las de otros métodos de compresión de audio.Este trabajo ha sido financiado parcialmente por la Fundación Séneca de la Región de Murcia y el Ministerio de Ciencia y Tecnología, mediante la concesión de proyectos PB/63/FS/02 y TIC2003-09400-C04-02, respectivamente.Escuela Técnica Superior de Ingeniería de Telecomunicació

Modeling and Design of the Vector Control for a Three-Phase Single-Stage Grid-Connected PV System with LVRT Capability according to the Spanish Grid Code

This article deals with the vector control in dq axes of a three-phase grid-connected photovoltaic system with single-stage topology and low-voltage-ride-through capability. The photovoltaic generator is built using an array of several series-parallel Suntech PV modules and is modeled as a Lookup Table (two-dimensional; 2-D). The requirements adopted when grid voltage sags occur are based in both the IEC 61400-21 European normative and the allowed amount of reactive power to be delivered according to the Spanish grid code, which avoids the disconnection of the inverter under grid faults by a limitation in the magnitude of the three-phase output inverter currents. For this, the calculation of the positive- and negative-sequences of the grid voltages is made and a conventional three-phase Phase-Locked Loop is used for the inverter-grid synchronization, allowing the control of the active and reactive powers solely with the dq components of the inverter currents. A detailed enhanced flowchart of the control algorithm with low-voltage-ride-through capability is presented and several simulations and experiments using Matlab/SIMULINK and the Controller Hardware-in-the-Loop simulation technique, respectively, are run for several types of one- and three-phase voltage sags in order to validate its behavior

Enhanced Control of Three-Phase Grid-Connected Renewables with Fault Ride-Through Capability under Voltage Sags

The uninterruptible operation of grid-connected renewables under the occurrence of grid voltage sags is addressed in this work. This is achieved due to the incorporation of an enhanced control algorithm of a renewable source. The low-voltage ride-through algorithm was developed in accordance to the voltage profile introduced by IEC 61400-21 regarding grid voltage sags. To guarantee continuous operation of the renewable agent during voltage sags, not only instantaneous reactive power but also instantaneous active power under moderate voltage sags was injected to the utility grid fulfilling grid code requirements. A dual second-order generalized integrator frequency-locked loop synchronization algorithm was used to estimate the system’s frequency, together with the positive and the negative sequences of the three-phase utility grid voltages when unbalanced sags occurred. The current control was made in a stationary reference frame by using proportional-resonant regulators, and a DC voltage source was used to emulate the primary energy from any type of renewable system. The validation of the proposed control algorithm was conducted for a three-phase grid-connected renewable system with an apparent power of 500 kVA. The results from several experimental tests demonstrated the proper behavior of the enhanced algorithm