Open Access
Nueva topología de inversor de media tensión con conexión en cascada y funcionamiento secuencial para grandes plantas fotovoltaicas: operación, control, dimensionado óptimo y validación experimental
(2021) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
El contexto energético actual se caracteriza por un fuerte crecimiento de las energías renovables, motivado por el notable descenso de coste que han experimentado en los últimos años, especialmente en el caso de la energía solar fotovoltaica. Las plantas fotovoltaicas de gran tamaño son las que presentan un menor coste, utilizándose tradicionalmente en ellas la configuración de inversor central. Sin embargo, esta configuración, por sus propias características, tiene un potencial limitado en cuanto a futuras reducciones de costes. En esta tesis, se propone una nueva topología de conversión con la configuración de inversor en cascada que, entre otras ventajas, permite la reducción del cableado de la planta fotovoltaica. Además, gracias a su funcionamiento secuencial, reduce el número de etapas de conversión en comparación con las soluciones investigadas hasta la fecha. Asimismo, su modulación hace que se realicen conmutaciones sin pérdidas en todas sus etapas de conversión. Las principales líneas de investigación que se abordan en esta tesis son: - Análisis de la configuración de inversor central en una gran planta fotovoltaica; - Estudio de las ventajas de la configuración de inversor en cascada y realización de un estado del arte de esta configuración; - Propuesta de la nueva topología de conversión; - Análisis del funcionamiento y desarrollo del control de la topología propuesta; - Validación experimental de la topología propuesta; - Estudio de la estabilidad de un sistema de control: formulación de un nuevo criterio de estabilidad y aplicación al diseño de los lazos de control de la topología propuesta; - Dimensionado óptimo de un sistema fotovoltaico con la topología propuesta y evaluación de su competitividad.
Open Access
Active control for medium-frequency transformers flux-balancing in a novel three-phase topology for cascaded conversion structures
(IEEE, 2020) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Navarrete, Manuel; Balda Belzunegui, Julián; González Senosiain, Roberto; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Efficiency and power density are important parameters in the design of power electronics converters. In many applications, low-frequency transformers are being substituted for medium-frequency and high-frequency transformers in order to reduce the volume and therefore the cost of the transformer. However, preventing their saturation is a complex task. This paper studies the medium-frequency transformers' flux balancing in a novel three-phase topology for cascaded conversion structures.Based on the modulation technique of the converter, a method to directly measure the magnetizing current of the medium-frequency transformers is proposed in this paper. A control loop to regulate the dc value of the magnetizing current is also designed and developed. Simulation results validate the correct operation of the control loop, which prevents the transformer saturation.
Open Access
Novel three-phase topology for cascaded multilevel medium-voltage conversion systems in large-scale PV plants
(IEEE, 2020) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Balda Belzunegui, Julián; González Senosiain, Roberto; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Solar photovoltaic renewable energy systems are expanding in the power sector thanks to its increasingly competitive prices. Traditionally, large-scale PV plants have reduced their cost by increasing the power ratings of the inverters and the line-frequency transformers. However, cost-reduction limits of large-scale PV plants are being reached. Cascaded converters have appeared as a solution to continue reducing the cost of large PV plants as they reduce the wiring cost. In this paper, a novel three-phase topology for cascaded conversion structures is proposed. It only has 2 conversion steps, one without switching losses. Hence, it increases the efficiency and reduces the cost of the previously proposed cascaded conversion systems. The topology is patent pending.
Open Access
Medium-voltage cascaded sequential topology for large-scale PV plants
(Institute of Electrical and Electronics Engineers Inc., 2021) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Balda Belzunegui, Julián; Navarrete, Manuel; González Senosiain, Roberto; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Photovoltaic (PV) conversion systems are in continuous development due to their increasingly competitive prices. The traditional configuration of large-scale PV plants is based on high-power central inverters, which have reduced their cost by increasing their power rating. However, this cost reduction is expected to saturate in the near future, mainly due to an increase in the cost of the dc wiring. Cascaded conversion systems have appeared as potential solutions to continue reducing the PV plant cost. They consist of several conversion units whose ac outputs are connected in series. This enables the power-rating reduction of each individual conversion unit, while maintaining the power rating of the conversion structure. Thus, the conversion units are placed closer to the PV panels, reducing the dc wiring cost. In this paper, a novel three-phase topology for medium-voltage cascaded conversion systems is presented. The proposed topology is formed of several conversion units, each one with a reduced number of conversion stages, namely, dc/ac, medium-frequency isolation and ac/ac. Moreover, thanks to its sequential operation and modulation technique, zero-voltage switching and zero-current switching are achieved in all conversion stages. In this way, with respect to the configuration with central inverters, the proposed topology has the advantages of cascaded conversion systems. In comparison to previously investigated cascaded topologies, the proposed topology also presents promising characteristics, representing a potential cost reduction and efficiency increase. An experimental validation of the topology is carried out in a laboratory prototype consisting of three conversion units.
Open Access
Control design and stability analysis of power converters: the MIMO generalized bode criterion
(IEEE, 2020) Samanes Pascual, Javier; Urtasun Erburu, Andoni; Barrios Rípodas, Ernesto; Lumbreras Magallón, David; López Taberna, Jesús; Gubía Villabona, Eugenio; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Three-phase dynamic systems and multiphase generators are frequently modeled and controlled in the synchronous reference frame. To properly model the cross-coupling terms in this reference frame, complex vector theory and transfer function matrices are commonly applied, obtaining multiple-input multiple-output (MIMO) dynamic models. The stability of MIMO systems can be assessed through the Nyquist generalized stability criterion. However, the use of the Nyquist diagram complicates the controller design. The Bode diagram is a more intuitive tool for the controller design; however, the Bode stability criterion is not applicable to MIMO systems. In this article, the MIMO generalized Bode criterion is proposed. Since this stability criterion is based on the Nyquist generalized stability criterion, it can be applied to any system. Furthermore, it is simple to use, as it only requires information contained in the open-loop transfer matrix and the Bode diagram. The proposed stability criterion thus offers an interesting tool for the controller design procedure in MIMO systems, as it is shown in this article for two common applications: the current control loop of a power converter, a 2 × 2 system, and the current control loop of two independent power converters in parallel, a 4 × 4 system.