Robust Modified Flower Pollination Algorithm for Power Quality Enhancement in an Autonomous 31-Level Cascaded H-Bridge Photovoltaic Inverter with Partial Shading Conditions

The effect of global warming and the scarcity of fossil fuels has created an enormous problem in today’s era. To overcome such a problem, renewable energy sources, particularly solar energy, play a crucial role in meeting the developing need for power. However, the design of the Solar Photovoltaic (PV) system is interrupted by various factors such as the effect of temperature, isolation, aging, partial shading conditions, etc. Among all the factors mentioned, partial shading results in the significant diminution of power. To address this shading effect and enhance the flexibility of the PV system in terms of better utilization and energy extraction, a 31-Level Cascaded H-Bridge Multilevel Inverter (CHB-MLI) has been implemented to the autonomous PV system comprising of Maximum Power Point Tracking (MPPT) controller, boost converter and variable loads in MATLAB/Simulink architecture. To track maximum power from PV during varying irradiance and temperature and to further improve the system performance in terms of better convergence speed, an MPPT system with a Modified Flower Pollination Algorithm (MFPA) based PID controller has been proposed in this paper. To justify the suggested approach, the is-landed PV system is led to variation in irradiance and load. A detailed comparison of the proposed MFPA technique with classical control techniques has been meticulously discussed. The results obtained indicate that the suggested MFPA tuned PID with MLI outperforms the conventional methods in better system stability, reduced harmonics, and enhanced capacity to track maximum power from the PV system. In addition to this, the Total Harmonic Distortion (THD) using Fast Fourier Transform (FFT) has been found to verify IEEE-1547 power quality constraints. The values are found to be well within limits, thus justifying its real-time applications

High Granularity approaches for effective energy delivery from Photovoltaic Sources

Silicon solar cell technology is a fully mature technology but the need to compete with traditional and other renewable energy sources urges to improve the overall efficiency of a photovoltaic (PV) system by a significant amount. Regardless of the solar panel efficiency, the difference between the nominal performance of a PV system and the energy actually produced is quite high, and it can be quantified in the order of 20%. A loss term, often underestimated, depends on possible failure of the Maximum Power Point Tracking (MPPT) algorithms in the presence of multiple maximum power points in power-voltage characteristic, arising in mismatch conditions. This work proposes High Granularity (HG) approaches in order to improve the PV energy yield: a monitoring strategy, a modeling and a power flux control of the whole PV system, all performed at level of single elementary source (i.e., PV cell or PV panel). An innovative HG sensor infrastructure was developed, and the measurements were exploited to perform an automatic PV system reconfiguration, and to design an information based MPPT. Moreover, the data validated a circuit HG model describing the PV system at single cell level, which also accounts for the electrothermal effect. The model was exploited in an automatic tool which translates an AutoCAD project of a PV plant in an equivalent circuit netlist. Finally, the results were employed to investigate the effectiveness of distributed power conversion – in particular the efficiency of the multilevel cascaded H bridge converter controlled by means of an innovative strategy, which overcomes some issues related to the need of performing a distributed MPPT, was assessed

Real-Time Selective Harmonic Minimization for Multilevel Inverters Using Genetic Algorithm and Artificial Neural Network Angle Generation

This work approximates the selective harmonic elimination problem using Artificial Neural Networks (ANN) to generate the switching angles in an 11-level full bridge cascade inverter powered by five varying DC input sources. Each of the five full bridges of the cascade inverter was connected to a separate 195W solar panel. The angles were chosen such that the fundamental was kept constant and the low order harmonics were minimized or eliminated. A non-deterministic method is used to solve the system for the angles and to obtain the data set for the ANN training. The method also provides a set of acceptable solutions in the space where solutions do not exist by analytical methods. The trained ANN is a suitable tool that brings a small generalization effect on the angles\u27 precision and is able to perform in real time (50/60Hz time window)

Study and evaluation of distributed power electronic converters in photovoltaic generation applications

This research project has proposed a new modulation technique called “Local Carrier Pulse Width Modulation” (LC-PWM) for MMCs with different cell voltages, taking into account the measured cell voltages to generate switching sequences with more accurate timing. It also adapts the modulator sampling period to improve the transitions from level to level, an important issue to reduce noise at the internal circulating currents. As a result, the new modulation LC-PWM technique reduces the output distortion in a wider range of voltage situations. Furthermore, it effectively eliminates unnecessary AC components of circulating currents, resulting in lower power losses and higher MMC efficiency.Departamento de Tecnología ElectrónicaDoctorado en Ingeniería Industria

A Current-Source Modular Converter for Large-Scale Photovoltaic Systems

The world is shifting toward renewable energy sources (RESs) to generate clean energy and mitigate the stress of global warming caused by CO2 emissions in recent decades. Among several RES types, large-scale photovoltaic (LSPV) plants are a promising source for meeting ambitious clean energy targets and being part of power generation. With the progress of high-power modular inverters, new opportunities have arisen to integrate them into LSPV systems connected to medium-voltage (MV) grids to obtain high efficiency and reliability, better system flexibility, and improved electrical safety compared with string or central inverters. This thesis presents and implements a new current source three-phase modular inverter (TPMI) based on a novel dual-isolated SEPIC/CUK (DISC) converter. The TPMI is designed with a single power processing stage comprised of seriesconnected DISC submodules (SMs) to deliver MV into the utility grid. It outperforms conventional high-power inverters in terms of modularity, scalability, galvanic isolation compliance, and distributed maximum power point tracking (MPPT) capabilities. The DISC converter employed as an SM in the proposed TPMI generates bipolar output (i.e., both positive and negative voltages). In addition to having step-up and step-down capabilities with a continuous input current, this converter shares an input side inductor, thereby reducing the number of components. The DISC structure, modulation method, operation, novel state-space model, and parameter design procedure are analysed in details. Then, simulation results are presented to validate the theoretical and analytical analyses of the DISC converter. The proposed TPMI inverter is subsequently integrated into the LSPV grid connection to prove its suitability for such applications. In the theoretical analysis, the advantages of TPMI structure over conventional topologies are discussed. Then, the modulation technique, and operational concept are presented, followed by a dedicated control strategy is implemented by adding a system and SM-level controllers. The system controller is required for the generation of uniform duty ratios for all SMs in order to regulate the power transfer. The SM level controller is introduced to ensure equal current and voltage distribution between SMs and to compensate for minor discrepancies between the various parameters. The entire TPMI system is demonstrated through MATLAB and Simulink simulations, with the objective being to deliver the rated (1 MW) power from the PV modules under normal operation, uniform shading, and partial shading conditions and to match PV generation with the grid’s power demands. A downscaled 3-kW TPMI inverter was developed in the laboratory to validate its feasibility experimentally with its control strategy in different operating conditions. Finally, the TPMI performance is compared with selected current source inverter topologies, which shows that TPMI obtains good efficiency within the context of existing state-of-the-art current source converters. Then, the TPMI structure is modified by redesigning its DISC SMs, which provides several benefits, including a reduction in the number of switch devices operating at high frequency, thus decreasing switching losses, and an increase in efficiency. In this study, a half-cycle modulation (HCM) scheme is developed for the switches, and the operation of a modified DISC SM is analysed. Simulation and experimental results validate the performance of the modified TPMI topology and demonstrate its suitability for LSPV applications. According to the results of the comparison, the maximum power efficiency of the modified TPMI structure is 95.5%, which represents an improvement over the original TPMI structure

Effective Utilization of Battery Banks In Multi-Level Inverters for a Residential Photovoltaic Applications

Distributed generation is key to improve reliability, reduced emission and improve power quality. In spite of high initial cost PV is forefront in renewable energy generation. For a residential PV installed application complete utilization of battery banks is key to reduce grid dependency and improve reliability. The present work introduces a novel methodology which leads to reduce the grid dependency and improve reliability for customer by making effective use of battery banks. In order to achieve above objective it’s important to keep battery banks difference or state of charges with in a threshold limit. This objective is attained by switching/shifting isolated panels. Selection of isolated panels through optimization by considering irregularity of roof top and worst case conditions. In addition, a control strategy is developed for switching isolated panels depending on difference in discharge levels. In addition, to decrease grid reliance and improve reliability a switching pattern is developed for a household installed PV system considering generation and load pattern. The present work is verified in MATLAB/Simulink environment

Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

New Three Phase Photovoltaic Energy Harvesting System for Generation of Balanced Voltages in Presence of Partial Shading, Module Mismatch, and Unequal Maximum Power Points

The worldwide energy demand is growing quickly, with an anticipated growth rate of 48% from 2012 to 2040. Consequently, investments in all forms of renewable energy generation systems have been growing rapidly due to growth rate and climate concerns. Increased use of clean renewable energy resources such as hydropower, wind, solar, geothermal, and biomass is expected to noticeably alleviate many present environmental concerns associated with fossil fuel-based energy generation. In recent years, wind and solar energies have gained the most attention among all other renewable resources. As a result, both have become the target of extensive research and development for dynamic performance optimization, cost reduction, and power reliability assurance. The performance of Photovoltaic (PV) systems is highly affected by environmental and ambient conditions such as irradiance fluctuations and temperature swings. Furthermore, the initial capital cost for establishing the PV infrastructure is very high. Therefore, it is essential that the PV systems always harvest the maximum energy possible by operating at the most efficient operating point, i.e. Maximum Power Point (MPP), to increase conversion efficiency to reach 100% and thus result in lowest cost of captured energy. The dissertation is an effort to develop a new PV conversion system for large scale PV grid-connected systems which provides 99.8% efficacy enhancements compared to conventional systems by balancing voltage mismatches between the PV modules. Hence, it analyzes the theoretical models for three selected DC/DC converters. To accomplish this goal, this work first introduces a new adaptive maximum PV energy extraction technique for PV grid-tied systems. Then, it supplements the proposed technique with a global search approach to distinguish absolute maximum power peaks within multi-local peaks in case of partially shaded PV module conditions. Next, it proposes an adaptive MPP tracking (MPPT) strategy based on the concept of model predictive control (MPC) in conjunction with a new current sensor-less approach to reduce the number of required sensors in the system. Finally, this work proposes a power balancing technique for injection of balanced three-phase power into the grid using a Cascaded H-Bridge (CHB) converter topology which brings together the entire system and results in the final proposed PV power system. The developed grid connected PV solar system is evaluated using simulations under realistic dynamic ambient conditions, partial shading, and fully shading conditions and the obtained results confirm its effectiveness and merits comparted to conventional systems. The resulting PV system offers enhanced reliability by guaranteeing effective system operation under unbalanced phase voltages caused by severe partial shading

Recent Advances of Wind-Solar Hybrid Renewable Energy Systems for Power Generation: A Review

A hybrid renewable energy source (HRES) consists of two or more renewable energy sources, such as wind turbines and photovoltaic systems, utilized together to provide increased system efficiency and improved stability in energy supply to a certain degree. The objective of this study is to present a comprehensive review of wind-solar HRES from the perspectives of power architectures, mathematical modeling, power electronic converter topologies, and design optimization algorithms. Since the uncertainty of HRES can be reduced further by including an energy storage system, this paper presents several hybrid energy storage system coupling technologies, highlighting their major advantages and disadvantages. Various HRES power converters and control strategies from the state-of-the-art have been discussed. Different types of energy source combinations, modeling, power converter architectures, sizing, and optimization techniques used in the existing HRES are reviewed in this work, which intends to serve as a comprehensive reference for researchers, engineers, and policymakers in this field. This article also discusses the technical challenges associated with HRES as well as the scope of future advances and research on HRES