Peak current mode control of three-phase boost rectifiers in discontinuous conduction mode for small wind power generators

[EN] This paper presents a peak current mode control scheme of a boost rectifier with low distortion of the input current for wind power systems based on permanent magnet synchronous generators with variable speed operation. The three-phase boost rectifier is operated in discontinuous conduction mode (DCM), and power factor correction techniques are applied. It is shown that the DCM operation significantly reduces the total harmonic distortion of the currents in the permanent magnet synchronous generator, increasing the power factor of the system, so that the vibrations and mechanical stress of the generator are minimized. The characteristics of the DCM boost rectifier are studied considering: (1) the series resistance of the inductors; (2) the modeling and adjustment of peak current mode control yielding a stable loop; (3) the design of an input filter that reduces the switching noise in the currents of the generator.This work was supported by the Spanish Ministry of Science and Innovation under Grants ENE2006- 15521-C03-02 and ENE2009- 13998-C02-02. The first author thanks the support of the Instituto Politecnico Nacional (IPN) and of the Comision de Operacion y Fomento de Actividades Academicas (COFAA) to finance his stay at the Universidad Politecnica de Valencia (UPV).Carranza, O.; Garcerá, G.; Figueres Amorós, E.; González, L. (2010). Peak current mode control of three-phase boost rectifiers in discontinuous conduction mode for small wind power generators. Applied Energy. 87(8):2728-2736. https://doi.org/10.1016/j.apenergy.2010.02.010S2728273687

Maximum-power-point tracking with reduced mechanical stress applied to wind-energy-conversion-systems

[EN] This paper presents an improved maximum-power-point tracking algorithm for wind-energy-conversion-systems. The proposed method significantly reduces the turbine mechanical stress with regard to conventional techniques, so that both the maintenance needs and the medium time between failures are expected to be improved. To achieve these objectives, a sensorless speed control loop receives its reference signal from a modified Perturb&Observe algorithm, in which the typical steps on the reference speed have been substituted by a fixed and well-defined slope ramp signal. As a result, it is achieved a soft dynamic response of both the torque and the speed of the wind turbine, so that the whole system suffers from a lower mechanical stress than with conventional P&O techniques. The proposed method has been applied to a wind turbine based on a permanent magnet synchronous generator operating at variable speed, which is connected to the distribution grid by means of a back to back converter.González, L.; Figueres Amorós, E.; Garcerá, G.; Carranza, O. (2010). Maximum-power-point tracking with reduced mechanical stress applied to wind-energy-conversion-systems. Applied Energy. 87(7):2304-2312. doi:10.1016/j.apenergy.2009.11.030S2304231287

An adaptive synchronous-reference-frame phase-locked loop for power quality improvement in a polluted utility grid

Si el © es de IEEE cuando se deposite una versión de autor hay que poner el siguiente texto en "descripción": “© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, 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 component of this work in other works.”The proper operation of grid-connected power electronics converters needs using a synchronization technique to estimate the phase of the grid voltage. The performance of this synchronization technique is related to the quality of the consumed or delivered electric power. The synchronous-reference-frame phase-locked loop (SRF-PLL) has been widely used due to its ease of operation and robust behavior. However, the estimated phase can have a considerable amount of unwanted ripple if the grid voltage disturbances are not properly rejected. The aim of this paper is to propose an adaptive SRF-PLL which strongly rejects these disturbances even if the fundamental frequency of the grid voltage varies. This is accomplished by using several adaptive infinite-impulse-response notch filters, implemented by means of an inherently stable Schur-lattice structure. This structure is perfectly suited to be programmed in fixed-point DSPs (i.e., it has high mapping precision, low roundoff accumulation, and suppression of quantization limit cycle oscillations). The proposed adaptive SRF-PLL has been tested by means of the TI TMS320F2812 DSP. The obtained experimental results show that the proposed synchronization method highly rejects the undesired harmonics even if the fundamental harmonic frequency of a highly polluted grid voltage abruptly varies. © 2011 IEEE.This work was supported by the Spanish Ministry of Science and Innovation under Grants ENE2009-13998-C02-02 and ENE2006-15521-C03-02.González Espín, FJ.; Figueres Amorós, E.; Garcerá Sanfeliú, 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.2011.2166236S2718273159

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

Effects of the PWM carrier signals synchronization on the DC-link current in back-to-back converters

[EN] This paper presents a study about the synchronization effects of the PWM carrier signals of a back-to-back converter for grid connection of Wind Energy Conversion Systems based on Permanent Magnet Synchronous Generators. It is demonstrated by means of a spectral analysis that, with the proper synchronization of the carrier signals of both the rectifier and inverter stages, the rms value of the current through the DC-link capacitors is greatly reduced. As a result, the number of capacitors needed to build the back-to-back converter decreases, whereas its life cycle is expanded, so that the Wind Energy Conversion System becomes more cost effective. It is shown that the worst case occurs when the phase difference between both carrier signals is ±¿/2, yielding the highest rms value of the DC-link capacitors current. In that case the harmonic with the highest rms value is located at twice the switching frequency. The theoretical analysis is compared with experimental results from a 10 kW back-to-back converter in order to validate the effects of the carrier signals phase shift on the DC-link capacitors current.Luis Gerardo González Morales; Garcerá, G.; Figueres Amorós, E.; González-Medina, R. (2010). Effects of the PWM carrier signals synchronization on the DC-link current in back-to-back converters. Applied Energy. 87(8):2491-2499. doi:10.1016/j.apenergy.2010.02.023S2491249987

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

A Method to Enhance the Global Efficiency of High-Power Photovoltaic Inverters Connected in Parallel

[EN] Central inverters are usually employed in large photovoltaic farms because they offer a good compromise between costs and efficiency. However, inverters based on a single power stage have poor efficiency in the low power range, when the irradiation conditions are low. For that reason, an extended solution has been the parallel connection of several inverter modules that manage a fraction of the full power. Besides other benefits, this power architecture can improve the efficiency of the whole system by connecting or disconnecting the modules depending on the amount of managed power. In this work, a control technique is proposed that maximizes the global efficiency of this kind of systems. The developed algorithm uses a functional model of the inverters¿ efficiency to decide the number of modules on stream. This model takes into account both the power that is instantaneously processed and the maximum power point tracking (MPPT) voltage that is applied to the photovoltaic field. A comparative study of several models of efficiency for photovoltaic inverters is carried out, showing that bidimensional models are the best choice for this kind of systems. The proposed algorithm has been evaluated by considering the real characteristics of commercial inverters, showing that a significant improvement of the global efficiency is obtained at the low power range in the case of sunny days. Moreover, the proposed technique dramatically improves the global efficiency in cloudy days.This work is supported by the Spanish Ministry of Economy and Competitiveness (MINECO), the European Regional Development Fund (ERDF) under Grants ENE2015-64087-C2-2-R and RTI2018-100732-B-C21, and the Spanish Ministry of Education (FPU15/01274).Liberos-Mascarell, MA.; González-Medina, R.; Garcerá, G.; Figueres Amorós, E. (2019). A Method to Enhance the Global Efficiency of High-Power Photovoltaic Inverters Connected in Parallel. Energies. 12(11):1-19. https://doi.org/10.3390/en12112219S1191211Wu, H., Locment, F., & Sechilariu, M. (2019). Experimental Implementation of a Flexible PV Power Control Mechanism in a DC Microgrid. Energies, 12(7), 1233. doi:10.3390/en12071233Strzalka, A., Alam, N., Duminil, E., Coors, V., & Eicker, U. (2012). Large scale integration of photovoltaics in cities. Applied Energy, 93, 413-421. doi:10.1016/j.apenergy.2011.12.033Zhang, P., Li, W., Li, S., Wang, Y., & Xiao, W. (2013). Reliability assessment of photovoltaic power systems: Review of current status and future perspectives. Applied Energy, 104, 822-833. doi:10.1016/j.apenergy.2012.12.010Kim, Y. S., Kang, S.-M., & Winston, R. (2011). Modeling of a concentrating photovoltaic system for optimum land use. Progress in Photovoltaics: Research and Applications, 21(2), 240-249. doi:10.1002/pip.1176Müller, B., Hardt, L., Armbruster, A., Kiefer, K., & Reise, C. (2015). Yield predictions for photovoltaic power plants: empirical validation, recent advances and remaining uncertainties. Progress in Photovoltaics: Research and Applications, 24(4), 570-583. doi:10.1002/pip.2616Borrega, M., Marroyo, L., Gonzalez, R., Balda, J., & Agorreta, J. L. (2013). Modeling and Control of a Master–Slave PV Inverter With N-Paralleled Inverters and Three-Phase Three-Limb Inductors. IEEE Transactions on Power Electronics, 28(6), 2842-2855. doi:10.1109/tpel.2012.2220859Araujo, S. V., Zacharias, P., & Mallwitz, R. (2010). Highly Efficient Single-Phase Transformerless Inverters for Grid-Connected Photovoltaic Systems. IEEE Transactions on Industrial Electronics, 57(9), 3118-3128. doi:10.1109/tie.2009.2037654Mohd, A., Ortjohann, E., Morton, D., & Omari, O. (2010). Review of control techniques for inverters parallel operation. Electric Power Systems Research, 80(12), 1477-1487. doi:10.1016/j.epsr.2010.06.009Su, J.-T., & Liu, C.-W. (2013). A Novel Phase-Shedding Control Scheme for Improved Light Load Efficiency of Multiphase Interleaved DC–DC Converters. IEEE Transactions on Power Electronics, 28(10), 4742-4752. doi:10.1109/tpel.2012.2233220Ahn, Y., Jeon, I., & Roh, J. (2014). A Multiphase Buck Converter With a Rotating Phase-Shedding Scheme For Efficient Light-Load Control. IEEE Journal of Solid-State Circuits, 49(11), 2673-2683. doi:10.1109/jssc.2014.2360400Peng, H., Anderson, D. I., & Hella, M. M. (2013). A 100 MHz Two-Phase Four-Segment DC-DC Converter With Light Load Efficiency Enhancement in 0.18/spl mu/m CMOS. IEEE Transactions on Circuits and Systems I: Regular Papers, 60(8), 2213-2224. doi:10.1109/tcsi.2013.2239157Costabeber, A., Mattavelli, P., & Saggini, S. (2010). Digital Time-Optimal Phase Shedding in Multiphase Buck Converters. IEEE Transactions on Power Electronics, 25(9), 2242-2247. doi:10.1109/tpel.2010.2049374Sánchez Reinoso, C. R., Milone, D. H., & Buitrago, R. H. (2013). Simulation of photovoltaic centrals with dynamic shading. Applied Energy, 103, 278-289. doi:10.1016/j.apenergy.2012.09.040Muñoz, J., Martínez-Moreno, F., & Lorenzo, E. (2010). On-site characterisation and energy efficiency of grid-connected PV inverters. Progress in Photovoltaics: Research and Applications, 19(2), 192-201. doi:10.1002/pip.997Davila-Gomez, L., Colmenar-Santos, A., Tawfik, M., & Castro-Gil, M. (2014). An accurate model for simulating energetic behavior of PV grid connected inverters. Simulation Modelling Practice and Theory, 49, 57-72. doi:10.1016/j.simpat.2014.08.001Rampinelli, G. A., Krenzinger, A., & Chenlo Romero, F. (2014). Mathematical models for efficiency of inverters used in grid connected photovoltaic systems. Renewable and Sustainable Energy Reviews, 34, 578-587. doi:10.1016/j.rser.2014.03.047MathWorks Statistics and Machine Learning Toolboxhttps://www.mathworks.co

Analysis of the control structure of wind energy generation systems based on a permanent magnet synchronous generator

This paper presents the analysis of the two usual control structures for variable speed and fixed pitch wind energy generation systems, namely speed and torque control, to determine the most appropriate structure to improve both robustness and reliability of this kind of distributed generators. The study considers all the elements of a typical wind power generation system and it has been carried out in a general way, so that conclusions are independent of the kind of the AC/DC converter that it is used to process the energy at the output of the generator. Particular emphasis was placed on developing a model of the turbine where the mechanical torque is considered as a system variable and not an exogenous disturbance for the system, as in other previous studies. After showing that speed control presents several advantages in terms of stability and reliability, an experimental study of this technique was carried out by using a grid connected wind generation system, which is composed by a three-phase boost rectifier feeding the grid connected inverter. Other practical issues for the design of high efficient wind generation systems, like the use of a Kalman speed estimator to avoid the need of mechanical sensors, are also implemented in the prototype and discussed in the paper. (c) 2012 Elsevier Ltd. All rights reserved.The first author thanks the support of the Instituto Politecnico Nacional (IPN) and of the Comision de Operacion y Fomento de Actividades Academicas (COFAA). This work was supported by the Spanish Ministry of Science and Innovation under Grant ENE2009-13998-C02-02.Carranza Castillo, O.; Figueres Amorós, E.; Garcerá Sanfeliú, G.; González Medina, R. (2013). Analysis of the control structure of wind energy generation systems based on a permanent magnet synchronous generator. Applied Energy. 103:522-538. https://doi.org/10.1016/j.apenergy.2012.10.015S52253810

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