A low-cost photovoltaic emulator for static and dynamic evaluation of photovoltaic power converters and facilities

In testing maximum power point tracking (MPPT) algorithms running on electronic power converters for photovoltaic (PV) applications, either a PV energy source (PV module or PV array) or a PV emulator is required. With a PV emulator, it is possible to control the testing conditions with accuracy so that it is the preferred option. The PV source is modeled as a current source; thus, the emulator has to work as a current source dependent on its output voltage. The proposed emulator is a buck converter with an average current mode control loop, which allows testing the static and dynamic performance of PV facilities up to 3 kW. To validate the concept, the emulator is used to evaluate the MPPT algorithm of a 230-W experimental microinverter working from a single PV module.This work is supported by the Spanish Ministry of Science and Innovation under grant ENE2009-13998-C02-02.González Medina, R.; Patrao Herrero, I.; Garcerá Sanfeliú, G.; Figueres Amorós, E. (2014). A low-cost photovoltaic emulator for static and dynamic evaluation of photovoltaic power converters and facilities. Progress in Photovoltaics. 22(2):227-241. https://doi.org/10.1002/pip.2243S227241222Prapanavarat, C., Barnes, M., & Jenkins, N. (2002). Investigation of the performance of a photovoltaic AC module. IEE Proceedings - Generation, Transmission and Distribution, 149(4), 472. doi:10.1049/ip-gtd:20020141Durán, E., Andújar, J. M., Galán, J., & Sidrach-de-Cardona, M. (2009). Methodology and experimental system for measuring and displayingIâ Vcharacteristic curves of PV facilities. Progress in Photovoltaics: Research and Applications, 17(8), 574-586. doi:10.1002/pip.909Piliougine, M., Carretero, J., Mora-López, L., & Sidrach-de-Cardona, M. (2011). Experimental system for current-voltage curve measurement of photovoltaic modules under outdoor conditions. Progress in Photovoltaics: Research and Applications, 19(5), 591-602. doi:10.1002/pip.1073Sanchis, P., López, J., Ursúa, A., Gubía, E., & Marroyo, L. (2007). On the testing, characterization, and evaluation of PV inverters and dynamic MPPT performance under real varying operating conditions. Progress in Photovoltaics: Research and Applications, 15(6), 541-556. doi:10.1002/pip.763Kjaer, 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.2005.853371Kondrath, N., & Kazimierczuk, M. K. (2012). Comparison of Wide- and High-Frequency Duty-Ratio-to-Inductor-Current Transfer Functions of DC–DC PWM Buck Converter in CCM. IEEE Transactions on Industrial Electronics, 59(1), 641-643. doi:10.1109/tie.2011.2134053Tan, 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.2004.827707Villalva, M. G., Gazoli, J. R., & Filho, E. R. (2009). Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays. IEEE Transactions on Power Electronics, 24(5), 1198-1208. doi:10.1109/tpel.2009.2013862Shengyi Liu, & Dougal, R. A. (2002). Dynamic multiphysics model for solar array. IEEE Transactions on Energy Conversion, 17(2), 285-294. doi:10.1109/tec.2002.1009482Mekki, H., Mellit, A., Kalogirou, S. A., Messai, A., & Furlan, G. (2010). FPGA-based implementation of a real time photovoltaic module simulator. Progress in Photovoltaics: Research and Applications, 18(2), 115-127. doi:10.1002/pip.950Mohan N Undeland T Robbins W Power electronics: converters, applications and design (3rd edn) 2003Garcera, G., Figueres, E., Pascual, M., & Benavent, J. M. (2004). Robust model following control of parallel buck converters. IEEE Transactions on Aerospace and Electronic Systems, 40(3), 983-997. doi:10.1109/taes.2004.1337469Vorperian, V. (1990). Simplified analysis of PWM converters using model of PWM switch. Continuous conduction mode. IEEE Transactions on Aerospace and Electronic Systems, 26(3), 490-496. doi:10.1109/7.106126Packiam, P., Jain, N. K., & Singh, I. P. (2011). Microcontroller-based simple maximum power point tracking controller for single-stage solar stand-alone water pumping system. Progress in Photovoltaics: Research and Applications, n/a-n/a. doi:10.1002/pip.1207Chuanzong F Shiping S Simulation studying of MPPT control by a new method for photovoltaic power system Electrical and Control Engineering (ICECE), 2011 International Conference on 2011 10.1109/ICECENG.2011.605791

Dual Input Microinverter for Tandem Cells

For every solar panel, there is an inverter which transforms the harvested DC electricity into AC electricity so that it can connect to the grid and power household appliances. In this project, we examined a tandem solar cell being designed by Iris Photovoltaics which has two layers with two distinct outputs, and we explored several solutions to create a microinverter which can handle dual inputs from the tandem PV and combine them into a single AC output. To examine the viability of such a microinverter, we designed and simulated the DC-DC combination portion of the specialized dual input microinverter, resulting in a working circuit simulation using flyback transformers which can take two DC inputs at different voltage and current levels and combine them together into a single high voltage on the DC bus, ready to be transformed into AC. We also purchased an already existing dual input microinverter and tested it by connecting it with two different solar panels and measuring its performance, however we could not obtain useful results because it did not function as intended. Overall the dual input microinverter is an interesting technology involving maximum power point tracking, DC combination, and power electronics. It has a multitude of applications, and it fits perfectly with the 4-terminal tandem solar module being developed by Iris Photovoltaics

High-Efficiency Isolated Photovoltaic Microinverter Using Wide-Band Gap Switches for Standalone and Grid-Tied Applications

An isolated photovoltaic micro-inverter for standalone and grid-tied applications is designed and implemented to achieve high efficiency. System configuration and design considerations, including the proposed active-clamp forward-flyback resonant converter for the DC-DC stage and a dual-frequency full-bridge inverter for the DC-AC stage, are analyzed and discussed. A prototype microinverter system is built and tested. Experimental results verify the feasibility of the proposed system, which achieves 95% power conversion efficiency at full load

Smart Home Energy Controller

The purpose of this project was to design a prototype device that could address the two main issues the team identified with existing residential solar systems: specifically, the inability to use solar power when the grid is offline and the inability to dynamically allocate power in a reconfigurable manner. The team researched solar system topologies and components then built and tested a proof of concept device referred to as smart home energy controller. This report details the current state of solar PV system architectures, identifies current PV system design limitations, and explains the team’s proposed solutions. The group also addresses the final PV system designs and the technical challenges encountered with the technologies used in the prototype test setup

Single-Stage Grid-Connected Forward Microinverter with Boundary Mode Control

This paper presents a microinverter to be integrated into a solar module. The proposed solution combines a forward converter and a constant off-time boundary mode control, providing MPPT capability and unity power factor in a single-stage converter. The transformer structure of the power stage remains as in the classical DC-DC forward converter. Transformer primary windings are utilized for power transfer or demagnetization depending on the grid semi-cycle. Furthermore, bidirectional switches are used on the secondary side allowing direct connection of the inverter to the grid. Design considerations for the proposed solution are provided, regarding the inductance value, transformer turns ratio and frequency variation during a line semi-cycle. The decoupling of the twice the line frequency power pulsation is also discussed, as well as the maximum power point tracking (MPPT) capability. Simulation and experimental results for a 100W prototype are enclose

Smart Two-Stage Solar Microinverter

The goal of the project was to design and build a two-stage solar microinverter that can be used as a testbench for MPPT algorithms and control structures. Testing these algorithms and control structures will give future researchers the ability to test their various ideas to further develop solar energy research. A prototype microinverter consisting of a flyback DC-DC converter and a full bridge DC-AC inverter was designed, assembled and tested. The converter and inverter sections function individually, but further work is needed to combine the two sections into a full microinverter

Analysis of active islanding detection methods for grid-connected microinverters for renewable energy processing

[EN] This paper presents the analysis and comparison of the main active techniques for islanding detection used in grid-connected microinverters for power processing of renewable energy sources. These techniques can be classified into two classes: techniques introducing positive feedback in the control of the inverter and techniques based on harmonics injection. Accurate PSIMTM simulations have been carried out in order to perform a comparative analysis of the techniques under study and to establish their advantages and disadvantages according to IEEE standards.This work was supported by the Spanish Ministry of Science and Innovation under Grant ENE2009-13998-C02-02.Trujillo Rodríguez, CL.; Velasco De La Fuente, D.; Figueres Amorós, E.; Garcerá, G. (2010). Analysis of active islanding detection methods for grid-connected microinverters for renewable energy processing. Applied Energy. 87(11):3591-3605. https://doi.org/10.1016/j.apenergy.2010.05.014S35913605871

Analysis, Design, and Control of a Single-Phase Single-Stage Grid-Connected Transformerless Solar Inverter

As energy utilization is increasing with the rise in the world’s power demand, the traditional energy sources are depleting at a high pace. It has led to attention drawn towards inexhaustible energy resources. There is a huge augmentation in the power generation from renewable energy sources (RES) like wind, solar, hydropower, biomass, etc. to reduce the stress on conventional energy sources like fossil fuels, oil, gas, etc. There has been a steep increase in interest for wind and solar energy systems. PV energy has been growing swiftly in the past two decades which made it most demanded power generation system based on RES. This worldwide requirement for solar energy has led to an immense amount of innovation and development in the Photovoltaic (PV) market. The Conventional grid-connected PV inverter was either with DC/DC converter or without DC/DC converter. These inverters were isolated using a transformer either on the grid (AC) side as a low-frequency transformer or as a high-frequency transformer on the DC side. Elimination of the transformer leads to a galvanic connection between the grid and PV module. This gives rise to the flow of leakage current which is disastrous for the system when it exceeds a specific value. Thus, minimization of this leakage current after the removal of the transformer has been an interesting topic explored by many researchers. Many topologies have been proposed targeting reduction in this leakage current either by 1.) Directly connecting the PV negative with neutral of utility grid or 2.) Disconnecting the PV panel side from AC side. This generally involved addition of more switches or diodes or supplementary branches to disconnect during the freewheeling period. Generally, the above-mentioned ways lead to a reduction in efficiency due to increased losses or complex circuitry. The motivation of this thesis is to design a transformerless inverter for single-phase PV grid-tied system with a smaller number of devices and still has minimum ground current. It discusses the prevailing inverter topologies in detail and then explains the modes of operation of the proposed inverter. A simple control strategy has been derived and passive elements of the inverter are designed. The simulation results presented have validated the theoretical claims. The experimental results which are similar to simulation results are evidence that the proposed topology is suitable for PV grid-tied systems. Also, the dynamic modeling of the inverter has been done to derive the plant transfer function. Then, the Proportional Resonant (PR) controller has been designed to ensure the flow of sinusoidal current into the grid with zero steady-state error and constant sinusoidal grid voltage irrespective of load change. The simulation and experimental results achieved high performance which makes this topology successful and promising for grid-tied PV systems

Grid-Tied Solar System

Distribution level solar energy generation has gained importance and popularity, because it helps create a sustainable electricity system while reducing the harmful environmental impacts our current power systems have. This project proposes an alternative energy source, a laboratory-scale grid-connected photovoltaic system. A KC120-1 solar panel produces 120 Watts maximum. A grid-tied solar power inverter does DC-to-AC conversion and minimizes energy transfer losses. The inverter also has an anti-islanding feature, which senses a power outage and prevents back-feeding through isolating the circuit. The circuit breakers isolate electrical components and protect the circuit. Schweitzer Engineering Laboratories SEL-751 feeder protection relay and SEL-735 power quality meter protect and monitor the feeder before joining the Microgrid Lab