Non-PLL Direct Power Control for a Single-Phase Grid-Connected Three-Level Inverter

The growing demand for clean, reliable renewable energy generation has led to the widespread adoption of solar energy as a source of electricity. Technological advancement aiding to reduce the cost of solar photovoltaic (PV) panels, as well as improvement in power electronics and control strategies for solar PV systems have also contributed to the growing popularity. For grid-connected solar systems to adequately meet future demand and grid requirements, the system must be reliable, and not affected by instability or distortions on the power grid. In this thesis, a control strategy for single-phase grid-connected inverters that can synchronize to the grid without a phase lock loop (PLL) is proposed. The PLL is an important device that is relied on for the synchronization of solar PV systems to the electrical grid. However, the PLL has an inherently complex design and its performance is often negatively affected if the grid voltage has poor quality. In addition, eliminating the use of PLL for synchronization can avoid the issue of slow dynamic response, higher harmonics, and increased computation complexity. The real and reactive power of the single-phase, three-level neutral point clamped (NPC) inverter is controlled by using a direct power control (DPC) strategy. A novel method of computing the power components of the single-phase inverter is proposed and this technique further improves the precision of the power components calculated by compensating the frequency and phase deviation compensation. Finally, simulations are carried out by using MATLAB/Simulink to demonstrate the effectiveness of the proposed methodology

Dynamic modeling of DC-DC converters with peak current control in double-stage photovoltaic grid-connected inverters

In photovoltaic (PV) double-stage grid-connected inverters a high-frequency DC-DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC-DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC-DC converter is regulated by the grid-connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small-signal model of the DC-DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230 W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC-DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full-bridge single-phase inverter. The time response of the whole system (DC-DC + inverter) is also shown to validate the concept. Copyright © 2011 John Wiley & Sons, Ltd. In photovoltaic (PV) double-stage gridconnected inverters a high-frequency DC-DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC-DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd.This work was supported by the Spanish Ministry of Science and Innovation (MICINN) under grant ENE2009-13998-C02-02. The company AUSTRIAMICROSYSTEMS co-financed this project.Garcerá Sanfeliú, G.; González Medina, R.; Figueres Amorós, E.; Sandía Paredes, J. (2012). Dynamic modeling of DC-DC converters with peak current control in double-stage photovoltaic grid-connected inverters. International Journal of Circuit Theory and Applications. 40(8):793-813. https://doi.org/10.1002/cta.756S793813408Carrasco, J. M., Franquelo, L. G., Bialasiewicz, J. T., Galvan, E., PortilloGuisado, R. C., Prats, M. A. M., … Moreno-Alfonso, N. (2006). Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey. IEEE Transactions on Industrial Electronics, 53(4), 1002-1016. doi:10.1109/tie.2006.878356Kjaer, 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.2005.853371Ridley, R. B. (1991). A new, continuous-time model for current-mode control (power convertors). IEEE Transactions on Power Electronics, 6(2), 271-280. doi:10.1109/63.76813Femia, N., Petrone, G., Spagnuolo, G., & Vitelli, M. (2005). Optimization of Perturb and Observe Maximum Power Point Tracking Method. IEEE Transactions on Power Electronics, 20(4), 963-973. doi:10.1109/tpel.2005.850975Hua, C., & Lin, J. (2004). A modified tracking algorithm for maximum power tracking of solar array. Energy Conversion and Management, 45(6), 911-925. doi:10.1016/s0196-8904(03)00193-6Tan, Y. T., Kirschen, D. S., & Jenkins, N. (2004). A Model of PV Generation Suitable for Stability Analysis. IEEE Transactions on Energy Conversion, 19(4), 748-755. doi:10.1109/tec.2004.827707Femia, N., Petrone, G., Spagnuolo, G., & Vitelli, M. (2009). A Technique for Improving P&O MPPT Performances of Double-Stage Grid-Connected Photovoltaic Systems. IEEE Transactions on Industrial Electronics, 56(11), 4473-4482. doi:10.1109/tie.2009.2029589Chiu, H.-J., Huang, H.-M., Yang, H.-T., & Cheng, S.-J. (2008). An improved single-stage Flyback PFC converter for high-luminance lighting LED lamps. International Journal of Circuit Theory and Applications, 36(2), 205-210. doi:10.1002/cta.404Chiu, H.-J., Yao, C.-J., & Lo, Y.-K. (2009). A DC/DC converter topology for renewable energy systems. International Journal of Circuit Theory and Applications, 37(3), 485-495. doi:10.1002/cta.475Martins DC Demonti R Photovoltaic Energy Processing for Utility Connected System 1292 1296 10.1109/IECON.2001.975968www.focus.ti.com/lit/ml/slup127/slup127.pdf2003 http://www.fairchildsemi.comEsram, T., & Chapman, P. L. (2007). Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques. IEEE Transactions on Energy Conversion, 22(2), 439-449. doi:10.1109/tec.2006.874230Liserre, M., Blaabjerg, F., & Hansen, S. (2005). Design and Control of an LCL-Filter-Based Three-Phase Active Rectifier. IEEE Transactions on Industry Applications, 41(5), 1281-1291. doi:10.1109/tia.2005.853373Liserre, M., Teodorescu, R., & Blaabjerg, F. (2006). Stability of photovoltaic and wind turbine grid-connected inverters for a large set of grid impedance values. IEEE Transactions on Power Electronics, 21(1), 263-272. doi:10.1109/tpel.2005.861185Figueres, E., Garcera, G., Sandia, J., Gonzalez-Espin, F., & Rubio, J. C. (2009). Sensitivity Study of the Dynamics of Three-Phase Photovoltaic Inverters With an LCL Grid Filter. IEEE Transactions on Industrial Electronics, 56(3), 706-717. doi:10.1109/tie.2008.2010175Ciobotaru M Teodorescu R Blaabjerg F Control of single-stage single-phase PV inverter P.1 P.10 10.1109/EPE.2005.219501Zmood, D. N., & Holmes, D. G. (2003). Stationary frame current regulation of PWM inverters with zero steady-state error. IEEE Transactions on Power Electronics, 18(3), 814-822. doi:10.1109/tpel.2003.810852Castilla, M., Miret, J., Matas, J., Garcia de Vicuna, L., & Guerrero, J. M. (2009). Control Design Guidelines for Single-Phase Grid-Connected Photovoltaic Inverters With Damped Resonant Harmonic Compensators. IEEE Transactions on Industrial Electronics, 56(11), 4492-4501. doi:10.1109/tie.2009.2017820Timbus A Teodorescu R Blaabjerg F Liserre M Synchronization methods for three phase distributed power generation systems 2474 2481 10.1109/PESC.2005.1581980Vorperian, V. (1990). Simplified analysis of PWM converters using model of PWM switch. II. Discontinuous conduction mode. IEEE Transactions on Aerospace and Electronic Systems, 26(3), 497-505. doi:10.1109/7.106127Reatti A Balzani M PWM switch model of a buck-boost converter operated under discontinuous conduction mode 667 670 10.1109/MWSCAS.2005.1594189Reatti, A., & Kazimierczuk, M. K. (2003). Small-signal model of PWM converters for discontinuous conduction mode and its application for boost converter. IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications, 50(1), 65-73. doi:10.1109/tcsi.2002.805709Lin, B.-R., Huang, C.-L., & Li, M.-Y. (2009). Novel interleaved ZVS converter with ripple current cancellation. International Journal of Circuit Theory and Applications, 37(3), 413-431. doi:10.1002/cta.480MIDDLEBROOK, R. D. (1975). Measurement of loop gain in feedback systems†. International Journal of Electronics, 38(4), 485-512. doi:10.1080/0020721750892042

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

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

A Novel Reduced Components Model Predictive Controlled Multilevel Inverter for Grid-Tied Applications

This paper presents an improved single-phase Multilevel Inverter (MLI) which is conceptualized to reduce power switches along with separate DC voltage sources. Compared with recent modular topologies, the proposed MLI employs a reduced number of components. The proposed inverter consists of a combination of two circuits, i.e., the level generation and polarity generation parts. The level generation part is used to synthesize different output voltage levels, while the polarity inversion is performed by a~conventional H-bridge circuit. The performance of the proposed topology has been studied using s single-phase seven-level inverter, which utilizes seven power switches and three independent DC voltage sources. Model Predictive Control (MPC) is applied to inject a sinusoidal current into the utility grid which exhibits low Total Harmonic Distortion (THD). Tests, including a~change in grid current amplitude as well as operation under variation in Power Factor (PF), have been performed to validate the good performance obtained using MPC. The effectiveness of the proposed seven-level inverter has been verified theoretically using MATLAB Simulink. In addition, Real-Time (RT) validation using the dSPACE-CP1103 has been performed to confirm the system performance and system operation using digital platforms. Simulation and RT results show improved THD at 1.23% of injected current

Direct usage of photovoltaic solar panels to supply a freezer motor with variable DC input voltage

In this paper, a single-phase photovoltaic (PV) inverter fed by a boost converter to supply a freezer motor with variable DC input is investigated. The proposed circuit has two stages. Firstly, the DC output of the PV panel that varies between 150 and 300 V will be applied to the boost converter. The boost converter will boost the input voltage to a fixed 300 V DC. Next, this voltage is supplied to the single-phase full-bridge inverter to obtain 230 V AC. In the end, The output of the inverter will feed a freezer motor. The PV panels can be stand-alone or grid-connected. The grid-connected PV is divided into two categories, such as with a transformer and without a transformer, a transformer type has galvanic isolation resulting in increasing the security and also provides no further DC current toward the grid, but it is expensive, heavy and bulky. The transformerless type holds high efficiency and it is cheaper, but it suffers from leakage current between PV and the grid. This paper proposes a stand-alone direct use of PV to supply a freezer; therefore, no grid connection will result in no leakage current between the PV and Grid. The proposed circuit has some features such as no filtering circuit at the output of the inverter, no battery in the system, DC-link instead of AC link that reduces no-loads, having a higher efficiency, and holding enough energy in the DC-link capacitor to get the motor started. The circuit uses no transformers, thus, it is cheaper and has a smaller size. In addition, the system does not require a complex pulse width modulation (PWM) technique, because the motor can operate with a pulsed waveform. The control strategy uses the PWM signal with the desired timing. With this type of square wave, the harmonics (5th and 7th) of the voltage are reduced. The experimental and simulation results are presented to verify the feasibility of the proposed strategy

Multilevel single phase isolated inverter with reduced number of switches

This paper proposes a cascaded single phase multilevel inverter using an off-the-shelf three-phase inverter and transformer. The concept is based on a cascaded connection of two inverter legs using a typical three phase inverter in such a way that the third leg is shared between the other two phases. The cascaded connection is achieved through an integrated series transformer with a typical three-phase transformer core. Utilization of a special transformer design has been previously proposed in the Custom Power Active Transformer. However, cascaded connection of inverter legs has not been previously investigated with such a concept. In this way, a three-leg inverter and a three-phase transformer are converted into an isolated multilevel single-phase inverter based on an unique configuration and modulation technique.Postprint (author's final draft

Integrated series transformer in cascade converters for photovoltaic energy systems

This paper proposes a novel configuration for photovoltaic applications based on a cascade converter topology. The series connection between modules is achieved through the magnetic core of the integrated series transformer, therefore an inherent isolation is provided without the requirement of a dc-dc conversion stage. Such isolation approach between each module allows operation at high voltage levels without harming the PV panel insulation. The main principles that support this proposal, as well as, simulation results are presented to validate the configuration.Peer ReviewedPostprint (author's final draft

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15