Concepción e integración en microrredes residenciales de inversores multinivel sin transformador de aislamiento con extracción simultánea de la máxima potencia de múltiples generadores fotovoltaicos

[EN] Multilevel inverters are being used in high-power applications, but the use of those topologies in small-power photovoltaic power plants presents some advantages. In this Thesis it is proposed a transformerless grid-connected single-phase photovoltaic inverter topology, called NPC+GCC, based on a multilevel topology. The characteristics of the NPC+GCC are of great interest for grid-connected transformerless inverters. It is demonstrated that that topology generates a very low capacitive leakage current, which is well below the limits stablished by the DIN VDE 0123-1-1 norm. The NPC+GCC topology permits the connection of a pair of photovoltaic sources on its input, getting the maximum power of both sources simultaneously. The efficiency of the power electronic converter is very high, since cascaded power stages are not used. This feature is of great interest in photovoltaic generation in urban areas because of the partial shadowing of the photovoltaic modules. Partial shadowing significantly deteriorates the energy harvesting. The double maximum power point tracking of the NPC+GCC reduces the effects of partial shadowing. Moreover, the inverter has been designed for working in distributed generation microgrids, an upcoming scenario. The main features of the inverter, transformerless and with a double maximum power point tracking, are especially relevant for power generation in the context of microgrids. The design has been validated by means of the construction and experimental study of an NPC+GCC converter with a nominal power of 5kW.[ES] Los inversores multinivel se utilizan de forma habitual en aplicaciones de gran potencia, pero la aplicación de las topologías multinivel en la generación fotovoltaica de pequeña potencia presenta algunas ventajas de interés. Se propone una topología de inversor fotovoltaico monofásico de inyección a red sin transformador, basada en las topologías multinivel, llamada NPC+GCC. Esta topología presenta características de gran interés para su uso como inversor sin transformador directamente conectado a la red eléctrica. Se estudia su tensión de modo común, y cómo esta genera una corriente de derivación capacitiva que se mantiene muy por debajo de los límites permitidos por la normativa. La topología NPC+GCC permite la conexión de dos generadores fotovoltaicos en su entrada, sobre los que efectuará una búsqueda del punto de máxima potencia de manera totalmente independiente y con un elevado rendimiento y fiabilidad, ya que no utiliza convertidores conectados en cascada para realizar esta función. Esta característica es de especial interés para la generación fotovoltaica en entornos urbanos, pues frecuentemente aparecen sombreados parciales sobre los módulos fotovoltaicos, que pueden deteriorar significativamente el aprovechamiento energético. El doble seguimiento del punto de máxima potencia permite reducir la influencia del sombreado parcial. Además, el inversor está diseñado para funcionar en microrredes de generación distribuida, adaptando así la generación fotovoltaica al nuevo escenario que está naciendo en la actualidad. Las principales características del inversor (sin transformador y con doble seguimiento del punto de máxima potencia) son de especial relevancia para la generación en el entorno de microrredes. El diseño se ha validado mediante la construcción y experimentación de un convertidor NPC+GCC de potencia nominal 5kW.[CA] Els inversors multinivell s'utilitzen de forma habitual en aplicacions de gran potència, però l'aplicació de les topologies multinivell en la generació fotovoltaica de petita potència presenta alguns avantatges d'interès. Proposem una topologia d'inversor fotovoltaic monofàsic d'injecció a xarxa sense transformador, basada en topologies multinivell, anomenada NPC+GCC. Aquesta topologia presenta característiques de gran interès per l'ús com a inversor sense transformador directament connectat a la xarxa elèctrica. N'estudiem la tensió de mode comú, i com aquesta genera un corrent de derivació capacitiu que es manté molt per davall dels límits permesos per la normativa. La topologia NPC+GCC permet la connexió de dos generadors fotovoltaics en l'entrada, sobre els quals efectuarà una cerca del punt de màxima potència de manera totalment independent i amb una elevada eficiència i fiabilitat, ja que no usa convertidors connectats en sèrie per a dur a terme aquesta funció. Aquesta característica és d'interès especial per a la generació fotovoltaica en entorns urbans, ja que freqüentment apareixen ombrejats parcials als mòduls fotovoltaics, que poden deteriorar significativament l'aprofitament energètic. El doble seguiment del punt de màxima potència permet reduir la influència de l'ombrejat parcial. A més, l'inversor està dissenyat per a funcionar en microxarxes de generació distribuïda, i així la generació fotovoltaica s'adapta al nou escenari que està naixent en l'actualitat. Les principals característiques de l'inversor (sense transformador i amb doble seguiment del punt de màxima potència) són d'especial rellevància per a la generació en l'entorn de microxarxes. El disseny ha sigut validat per mitjà de la construcció i l'experimentació d'un convertidor NPC+GCC de potència nominal 5kW.Patrao Herrero, I. (2015). Concepción e integración en microrredes residenciales de inversores multinivel sin transformador de aislamiento con extracción simultánea de la máxima potencia de múltiples generadores fotovoltaicos [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52023TESI

Grid-tie inverter topology with maximum power extraction from two photovoltaic arrays

This study presents a transformerless topology for a grid-tied single-phase inverter capable of performing the simultaneous maximum power point tracking of two independent and series connected photovoltaic sources. This topology is derived from the neutral point clamped multilevel inverter in half-bridge configuration. The use of a half-bridge topology reduces the leakage current to very low values, whereas the multilevel topology presents an output voltage quality similar to that of a full-bridge inverter. To simultaneously track the maximum power of both photovoltaic sources, a generation control circuit is used. With this topology, it is possible to improve the performance of the converter under partial shadowing conditions, very common in photovoltaic facilities operating in residential areas. A 5 kW prototype of this topology has been implemented and tested in the laboratory.This work is supported by the Spanish Ministry of Science and Innovation under grants ENE2009-13998-C02-02 and ENE2012-37667-C02-01.Patrao Herrero, I.; Gabriel Garcerá; Figueres Amorós, E.; González Medina, R. (2014). Grid-tie inverter topology with maximum power extraction from two photovoltaic arrays. Renewable Power Generation, IET. 8(6):638-648. doi:10.1049/iet-rpg.2013.0143S63864886Bevrani, H., Ghosh, A., & Ledwich, G. (2010). Renewable energy sources and frequency regulation: survey and new perspectives. IET Renewable Power Generation, 4(5), 438. doi:10.1049/iet-rpg.2009.0049Zhu, J., Bründlinger, R., Mühlberger, T., Betts, T. R., & Gottschalg, R. (2011). Optimised inverter sizing for photovoltaic systems in high-latitude maritime climates. IET Renewable Power Generation, 5(1), 58. doi:10.1049/iet-rpg.2009.0162Amoiralis, E. I., Tsili, M. A., & Kladas, A. G. (2012). Power Transformer Economic Evaluation in Decentralized Electricity Markets. IEEE Transactions on Industrial Electronics, 59(5), 2329-2341. doi:10.1109/tie.2011.2157291Bowtell, L., & Ahfock, A. (2010). Direct current offset controller for transformerless single-phase photovoltaic grid-connected inverters. IET Renewable Power Generation, 4(5), 428. doi:10.1049/iet-rpg.2009.0043Patrao, I., Figueres, E., González-Espín, F., & Garcerá, G. (2011). Transformerless topologies for grid-connected single-phase photovoltaic inverters. Renewable and Sustainable Energy Reviews, 15(7), 3423-3431. doi:10.1016/j.rser.2011.03.034Kjaer, S. B., Pedersen, J. K., & Blaabjerg, F. (2005). A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules. IEEE Transactions on Industry Applications, 41(5), 1292-1306. doi:10.1109/tia.2005.853371Puttgen, H. B., MacGregor, P. R., & Lambert, F. C. (2003). Distributed generation: Semantic hype or the dawn of a new era? IEEE Power and Energy Magazine, 1(1), 22-29. doi:10.1109/mpae.2003.1180357Nian, H., & Zeng, R. (2011). Improved control strategy for stand-alone distributed generation system under unbalanced and non-linear loads. IET Renewable Power Generation, 5(5), 323. doi:10.1049/iet-rpg.2010.0216Thomson, M., & Infield, D. G. (2007). Impact of widespread photovoltaics generation on distribution systems. IET Renewable Power Generation, 1(1), 33. doi:10.1049/iet-rpg:20060009Karatepe, E., Syafaruddin, & Hiyama, T. (2010). Simple and high-efficiency photovoltaic system under non-uniform operating conditions. IET Renewable Power Generation, 4(4), 354. doi:10.1049/iet-rpg.2009.0150Wang, Y.-J., & Hsu, P.-C. (2010). Analytical modelling of partial shading and different orientation of photovoltaic modules. IET Renewable Power Generation, 4(3), 272. doi:10.1049/iet-rpg.2009.0157López, Ó., Freijedo, F. D., Yepes, A. G., Fernández-Comesaña, P., Malvar, J., Teodorescu, R., & Doval-Gandoy, J. (2010). Eliminating Ground Current in a Transformerless Photovoltaic Application. IEEE Transactions on Energy Conversion, 25(1), 140-147. doi:10.1109/tec.2009.2037810Cavalcanti, M. C., Farias, A. M., Oliveira, K. C., Neves, F. A. S., & Afonso, J. L. (2012). Eliminating Leakage Currents in Neutral Point Clamped Inverters for Photovoltaic Systems. IEEE Transactions on Industrial Electronics, 59(1), 435-443. doi:10.1109/tie.2011.2138671Wu, T.-F., Chang, C.-H., Lin, L.-C., & Kuo, C.-L. (2011). Power Loss Comparison of Single- and Two-Stage Grid-Connected Photovoltaic Systems. IEEE Transactions on Energy Conversion, 26(2), 707-715. doi:10.1109/tec.2011.2123897Shimizu, T., Hirakata, M., Kamezawa, T., & Watanabe, H. (2001). Generation control circuit for photovoltaic modules. IEEE Transactions on Power Electronics, 16(3), 293-300. doi:10.1109/63.923760Gonzalez-Espin, F., Figueres, E., & Garcera, G. (2012). An Adaptive Synchronous-Reference-Frame Phase-Locked Loop for Power Quality Improvement in a Polluted Utility Grid. IEEE Transactions on Industrial Electronics, 59(6), 2718-2731. doi:10.1109/tie.2011.2166236Mastromauro, R. A., Liserre, M., & Dell’Aquila, A. (2012). Control Issues in Single-Stage Photovoltaic Systems: MPPT, Current and Voltage Control. IEEE Transactions on Industrial Informatics, 8(2), 241-254. doi:10.1109/tii.2012.2186973Delfino, F., Denegri, G. B., Procopio, R., & Invernizzi, M. (2012). Feedback linearisation oriented approach to Q–V control of grid connected photovoltaic units. IET Renewable Power Generation, 6(5), 324-339. doi:10.1049/iet-rpg.2011.0075Ishaque, K., & Salam, Z. (2013). A review of maximum power point tracking techniques of PV system for uniform insolation and partial shading condition. Renewable and Sustainable Energy Reviews, 19, 475-488. doi:10.1016/j.rser.2012.11.03

An Adaptive Control System for Three-Phase Photovoltaic Inverters Working in a Polluted andVariable Frequency Electric Grid

Theproportional+resonant (PR) controller has been proposed in the past as a suitable method to control the current generated by the grid-connected photovoltaic voltage source inverters. Due to the fact that information regarding the frequency of the grid is needed to use this control technique, the synchronous reference frame phase-locked loop (SRF-PLL) is commonly used. To assure that the total harmonic distortion of the injected current (THDi) meets the appropriate standards, even if the grid voltage is polluted and its frequency varies, an adaptive control strategy is presented in this paper. This control strategy can improve the behavior of both, the conventional SRF-PLL and the conventional PR controller, when they are used in a polluted grid with a time varying frequency. The experimental results obtained by means of a digitally controlled 10-kVA inverter, show up that the THDi of the injected current is improved when the proposed adaptive control strategy replaces the conventional one.This work was supported by the Spanish Ministry of Science and Innovation under Grant ENE2009-13998-C02-02. Recommended for publication by Associate Editor B. Lehman.González Espín, FJ.; Gabriel Garcerá; Patrao Herrero, I.; Figueres Amorós, E. (2012). An Adaptive Control System for Three-Phase Photovoltaic Inverters Working in a Polluted andVariable Frequency Electric Grid. IEEE Transactions on Power Electronics. 27(10):4248-4261. https://doi.org/10.1109/TPEL.2012.2191623S42484261271

An Adaptive Digital Control Technique for Improved Performance of Grid Connected Inverters

Grid connected voltage source inverters may be controlled in the stationary reference frame by means of the infinite impulse response (IIR) P+Resonat regulator. This regulator is able to correctly track fixed frequency sinusoidal references, but does not perform well if the frequency of the electric grid voltage is varied. In order to avoid the lack of precision to track variable frequency sinusoidal references, an adaptive IIR filter structure is proposed which offers good tracking properties even if the frequency of the grid voltage varies. This filter adapts its coefficients in real time and is inherently stable no matter the adaptation process, thus overcoming one of the most important drawbacks of the IIR filter structure. Furthermore, this structure is perfectly suited to be programmed in fixed point digital signal processors (DSPs) because of some important numeric properties, i.e., it has a high mapping precision and a low round-off accumulation, and it avoids quantization limit cycle oscillations. The proposed adaptive controller has been tested by means of the TI TMS320F2812 DSP. The obtained experimental results show up that this controller allows the correct tracking of a sinusoidal reference, even if this reference is time variant.This work was supported by the Spanish Ministry of Science and Innovation under Grant ENE2012-37667-C02-01. Paper no. TII-11-622.González Espín, FJ.; Patrao Herrero, I.; Figueres Amorós, E.; Gabriel Garcerá (2013). An Adaptive Digital Control Technique for Improved Performance of Grid Connected Inverters. IEEE Transactions on Industrial Informatics. 9(2):708-718. https://doi.org/10.1109/TII.2012.2225437S7087189

A Control Scheme to Suppress Circulating Currents in Parallel-Connected Three-Phase Inverters

[EN] The parallel operation of inverters has many benefits, such as modularity and redundancy. However, the parallel connection of inverters produces circulating currents that may result in malfunctions of the system. In this work, a control technique for the elimination of the low-frequency components of the circulating currents in grid-connected inverters is presented. The proposed control structure contains n - 1 zero-sequence control loops, with n being the number of inverters connected in parallel. Simulation and experimental results have been carried out on a prototype composed of two 5 kW inverters connected in parallel. The results have been obtained by considering the following mismatches between both inverters: inductance values of the grid filters, unbalance of the delivered power, and the use of different modulation techniques.This research was funded by the Spanish "Ministerio de Asuntos Economicos y Transformacion Digital" and the European Regional Development Fund (ERDF), under grants RTI2018100732-B-C21 and PID2021-122835OB-C22.Liberos, M.; González-Medina, R.; Patrao Herrero, I.; Garcerá, G.; Figueres Amorós, E. (2022). A Control Scheme to Suppress Circulating Currents in Parallel-Connected Three-Phase Inverters. Electronics. 11(22):1-23. https://doi.org/10.3390/electronics11223720123112

Synchronization of power inverters in islanded microgrids using an FM-modulated signal

"(c) 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works."A microgrid can operate in island mode, isolated from the main grid during certain time intervals. When operated in island mode, the electronic converters of the microgrid must keep the voltage and frequency of the microgrid inside the desired range. The converters of a microgrid can be classified into three groups: 1) grid-feeding; 2) grid-supporting; and 3) grid-forming power converters. The grid-forming converters operate as a voltage source, and require an external synchronization signal provided by the microgrid central controller. Both the noise and the delay in the synchronization signals received by the grid-forming converters are critical issues, which deteriorate the quality of the microgrid voltage and may overload those converters. The synchronization signals must be robust and suitable for operating in noisy environments. In this paper, the synchronization signal is frequency-modulated to be transmitted, being robust against noise. The transmission is done through an industrial RS-485 line with a low delay. The demodulation is performed with a low computational load by the control processors of the grid-forming power converters.This work was supported in part by the Spanish Ministry of Economy and Competitiveness under Grant ENE2015-64087-C2-2-R, and in part by the European Regional Development Fund.Patrao Herrero, I.; González Medina, R.; Marzal-Romeu, S.; Garcerá Sanfeliú, G.; Figueres Amorós, E. (2017). Synchronization of power inverters in islanded microgrids using an FM-modulated signal. IEEE Transactions on Smart Grid. 8(1):503-510. https://doi.org/10.1109/TSG.2016.2574038S5035108

Amplificadores operaciones fáciles aplicando el Teorema de Millman

En este video se explica cómo aplicar el Teorema de Millman a la resolución de circuitos con amplificadores operacionales, resultando en ecuaciones fáciles de resolver.https://polimedia.upv.es/visor/?id=d7804f80-b0ab-11ed-9a61-93bba90db995Patrao Herrero, I. (2023). Amplificadores operaciones fáciles aplicando el Teorema de Millman. http://hdl.handle.net/10251/19243

Entendiendo la hoja de características de un módulo fotovoltaico

Interpretar el contenido de la hoja de características de un módulo fotovoltaico comercial.https://polimedia.upv.es/visor/?id=df19bdb0-9528-11ed-8e51-154c12aba898Patrao Herrero, I. (2023). Entendiendo la hoja de características de un módulo fotovoltaico. http://hdl.handle.net/10251/19243

Diseño y evaluación de un inversor de potencia de 220W para conexión a red de módulos fotovoltáicos de 24 a 40V

Consulta en la Biblioteca ETSI Industriales (7941)[ES] Para ello habrá se deberán superar las siguientes fases: 1. Diseño y simulación de la etapa de potencia: filtro de conexión a red, semiconductores de potencia, cálculos térmicos, protecciones y circuitos de disparo. 2. Diseño y simulación del control en lazo cerrado del convertidor: PLL de sincronismo con la red, lazos de corriente y de tensión. 3. Diseño de las placas de circuito impreso para la construcción de un prototipo. 4. Evaluación final del inversor: rendimiento, distorsión de la corriente inyectada a red, factor de potencia...Patrao Herrero, I. (2009). Diseño y evaluación de un inversor de potencia de 220W para conexión a red de módulos fotovoltáicos de 24 a 40V. http://hdl.handle.net/10251/34288.Archivo delegad

Thévenin y Norton, una ayuda para la resolución de circuitos electrónicos

Simplificación de circuitos mediante la aplicación del teorema de Thévenin y del teorema de Nortonhttps://polimedia.upv.es/visor/?id=2add56e0-bcd8-11ed-9299-eba0e50de926Patrao Herrero, I. (2023). Thévenin y Norton, una ayuda para la resolución de circuitos electrónicos. http://hdl.handle.net/10251/19254