Non-uniform Irradiance Conditions Research Articles

Distributed PV Power Extraction Based on a Modified Interleaved SEPIC for Nonuniform Irradiation Conditions

Nonuniform irradiation of a photovoltaic (PV) source, consisting of series-connected modules with bypass diodes, results in multiple peaks in the power–voltage characteristics. This makes the maximum power point tracking (MPPT) difficult because the conventional MPPT algorithms can only deal with single power peak characteristics. This paper proposes a novel distributed MPPT (DMPPT) scheme based on an interleaved single-ended primary inductor converter (SEPIC) converter configuration for compensating the mismatch in characteristics of series-connected PV modules. The proposed scheme obviates the need for bypass diodes across the modules, resulting in single-peak power–voltage characteristics. The proposed DMPPT circuit is derived from an interleaved SEPIC converter that works on the “return energy” concept. The proposed configuration equalizes the voltages across PV modules of the string, resulting in their operating close to its maximum power point. Discontinuous conduction mode of operation is implemented, obviating the voltage-sensing requirements across modules, eliminating the reverse recovery loss of diodes and the turn-on loss of the main switch. The proposed DMPPT scheme uses a simple circuit with reduced control complexity and needs only a few passive elements and only one switching device, compared with the existing DMPPT schemes. The theoretical claims are validated with simulations and extensive hardware experiments.

Overview of Maximum Power Point Tracking Techniques for Photovoltaic Energy Production Systems

—A substantial growth of the installed photovoltaic systems capacity has occurred around the world during the last decade, thus enhancing the availability of electric energy in an environmentally friendly way. The maximum power point tracking technique enables maximization of the energy production of photovoltaic sources during stochastically varying solar irradiation and ambient temperature conditions. Thus, the overall efficiency of the photovoltaic energy production system is increased. Numerous techniques have been presented during the last decade for implementing the maximum power point tracking process in a photovoltaic system. This article provides an overview of the operating principles of these techniques, which are suited for either uniform or non-uniform solar irradiation conditions. The operational characteristics and implementation requirements of these maximum power point tracking methods are also analyzed to demonstrate their performance features.

Energy assessment of enhanced fixed low concentration photovoltaic systems

In order to exploit as much as possible the surfaces apt for installation of photovoltaic (PV) systems and also to keep the unit energy cost low (without increasing meaningfully capital and operation/maintenance costs), fixed low concentration systems (LCPVs) can be adopted, such systems are normally based on flat mirrors. LCPVs can be either fixed or tracked, but in this paper the fixed solution is investigated as it is a solution that can be largely exploited in urban and suburban contexts, as well as it represents a retrofit of existing PV plant. In order to mitigate the negative effects of partial shadowing of such systems, together with dust soiling and mismatching, this paper proposes an innovative solution for fixed LCPVs based on Distributed Maximum Power Point Tracking (DMPPT) at substring level, here called Enhanced LCPV (E-LCPV).To evaluate the energy performance improvement of the E-LCPV solution compared with conventional LCPVs, a simulation tool has been developed; it has as input the geographic, geometrical, optical and electrical characteristics of a fixed LCPV system and provides the daily production curves. The novelty of the tool here proposed is its ability to manage non-uniform irradiance conditions on a single PV module, which allows to compare the performance of the system with or without DMPPT at substring level.Specifically, four cases have been simulated: (a) without reflector and with bypass diode (conventional PV module); (b) without reflector but with DMPPT at the substring level; (c) with reflector and with bypass diode; (d) with reflector and with DMPPT at the substring level (E-LCPV).Comparative and parametric results are provided and discussed. Referring to Catania (Italy), results show that, in order to have advantages in using a E-LCPV, the PV module/reflector configuration should be accurately optimized in order to increase the power production, otherwise the cost of E-LCPVs can reduce drastically the advantages of using these kind of systems.

An Accurate Modeling of Photovoltaic System for Uniform and Non-Uniform Irradiance

Efficient modeling and simulation of photovoltaic (PV) systems has become more important due to the wide integration of solar energy in modern power systems. The equations describing the PV systems are transcendental , non-linear in nature, resulting in a slow and inefficient simulations for long-term analysis. This paper proposes a modified approach of modeling photovoltaic array for uniform and non-uniform irradiance condition. Initially for uniform irradiance condition, single diode model is used as equivalent circuit. An approach based on adaptively varying the value of series resistance is proposed to find the equivalent circuit parameters. The proposed model is simulated using MATLAB and results are validated with the experimental results obtained from the datasheet values and other models in the literature. The model is extended for non-uniform irradiance and the results are validated. The proposed model is more effective by adaptively varying the value of series resistance in order to decrease the computational burden and increase the level of accuracy.

An Ultrafast Maximum Power Point Setting Scheme for Photovoltaic Arrays Using Model Parameter Identification

Maximum power point tracking (MPPT) for photovoltaic (PV) arrays is essential to optimize conversion efficiency under variable and nonuniform irradiance conditions. Unfortunately, conventional MPPT algorithms such as perturb and observe (P&O), incremental conductance, and current sweep method need to iterate command current or voltage and frequently operate power converters with associated losses. Under partial overcast conditions, tracking the real MPP in multipeakP-IorP-Vcurve model becomes highly challenging, with associated increase in search time and converter operation, leading to unnecessary power being lost in the MPP tracking process. In this paper, the noted drawbacks in MPPT-controlled converters are addressed. In order to separate the search algorithms from converter operation, a model parameter identification approach is presented to estimate insolation conditions of each PV panel and build a real-time overallP-Icurve of PV arrays. Subsequently a simple but effective global MPPT algorithm is proposed to track the MPP in the overallP-Icurve obtained from the identified PV array model, ensuring that the converter works at the MPP. The novel MPPT is ultrafast, resulting in conserved power in the tracking process. Finally, simulations in different scenarios are executed to validate the novel scheme’s effectiveness and advantages.

Simple Moving Voltage Average Incremental Conductance MPPT Technique with Direct Control Method under Nonuniform Solar Irradiance Conditions

A new simple moving voltage average (SMVA) technique with fixed step direct control incremental conductance method is introduced to reduce solar photovoltaic voltage (VPV) oscillation under nonuniform solar irradiation conditions. To evaluate and validate the performance of the proposed SMVA method in comparison with the conventional fixed step direct control incremental conductance method under extreme conditions, different scenarios were simulated. Simulation results show that in most cases SMVA gives better results with more stability as compared to traditional fixed step direct control INC with faster tracking system along with reduction in sustained oscillations and possesses fast steady state response and robustness. The steady state oscillations are almost eliminated because of extremely smalldP/dVaround maximum power (MP), which verify that the proposed method is suitable for standalone PV system under extreme weather conditions not only in terms of bus voltage stability but also in overall system efficiency.

Voltage band based global MPPT controller for photovoltaic systems

This paper presents a new maximum power point tracking algorithm for PV systems useful in case of non-uniform irradiance conditions. This algorithm takes into account the number of bypass diodes in a PV string to calculate the voltage bands associated with the peak power points that appear in the power–voltage characteristic of the PV system. The main contribution of this study is to state that the global maximum power point can be tracked by considering only the possible voltage bands which can be found by using the proposed analytical equation in a simple manner. The algorithm is based in the evaluation and analysis of these voltage bands and in the selection of the PV system voltage related to the maximum power point of work. The proposed algorithm has been validated by means of simulation and also in an experimental study.

Artificial neural network based modified incremental conductance algorithm for maximum power point tracking in photovoltaic system under partial shading conditions

In solar PV (photovoltaic) system, tracking the module's MPP (maximum power point) is challenging due to varying climatic conditions. Moreover, the tracking algorithm becomes more complicated under the condition of partial shading due to the presence of multiple peaks in the power voltage characteristics. This paper presents a NN (neural network) based modified IC (incremental conductance) algorithm for MPPT (maximum power point tracking) in PV system. The PV system along with the proposed MPPT algorithm was simulated using Matlab/Simulink simscape tool box. The simulated system was evaluated under uniform and non-uniform irradiation conditions and the results are presented. For comparison, P&O (perturb and observe) and Fuzzy based Modified Hill Climbing algorithms were used for MPP tracking, and the results show that the proposed approach is effective in tracking the MPP under partial shading conditions. To validate the simulated system hardware implementation of the proposed algorithm was carried out using FPGA (Field Programmable Gate Array).

Optimization of photovoltaic energy production through an efficient switching matrix

This work presents a preliminary study on the implementation of a new system for power output maximization of photovoltaic generators under non-homogeneous conditions. The study evaluates the performance of an efficient switching matrix and the relevant automatic reconfiguration control algorithms. The switching matrix is installed between the PV generator and the inverter, allowing a large number of possible module configurations. PV generator, switching matrix and the intelligent controller have been simulated in Simulink. The proposed reconfiguration system improved the energy extracted by the PV generator under non-uniform solar irradiation conditions. Short calculation times of the proposed control algorithms allow its use in real time applications even where a higher number of PV modules is required.

An efficient fault diagnosis method for PV systems based on operating voltage-window

With the increasing use of photovoltaic (PV) systems, the research studies to improve the efficiency of PV systems have gained greater interest in recent years, especially under non-uniform operating conditions. However, there is a little attention on fault diagnosis of PV arrays. This paper develops and demonstrates a method that can efficiently detect the number of open and short circuit faults and discriminate between them and partial shading conditions. This method is based on only the measurement of operating voltage of PV string and ambient temperature. In that manner, the proposed method takes into consideration of the minimum number of sensors to reduce the cost of the system, as one of the main purposes of this study. The simulation and experimental results are presented to demonstrate the effectiveness of the proposed method under both uniform and non-uniform irradiance conditions.

Control of Single-Phase CHB Grid-Connected Photovoltaic System Under Non-uniform Irradiation Conditions

Abstract This paper proposes a novel MPPT method, which will provide a correct tracking direction under the condition of non-abrupt atmospheric changes, especially non-irradiation conditions. We also present a model predictive control method based on a cost function, which help to derive the predictions for each possible switching state. The control scheme obtained is capable of controlling the dc-link current to a desired MPPT reference current, while injecting sinusoidal current to the grid with reduced total harmonic distortion. Finally, the simulation results illustrate the effectiveness of our proposed method.

Performance enhancement of photovoltaic array through string and central based MPPT system under non-uniform irradiance conditions

Mismatching losses reduction of photovoltaic (PV) array has been intensively discussed through the increasing penetration of residential and commercial PV systems. Many causes of mismatching losses have been identified and plenty of proposed methods to solve this problem have been recently proposed. This paper deals with reducing method of mismatching losses due to the non-uniform irradiance conditions. It is well-known that a certain number of multiple peaks occur on the power–voltage curve as the number of PV modules in one-string increases under non-uniform operating conditions. Since the conventional control method only drives the operating points of PV system to the local maxima close to open circuit voltage, only small portion of power can be extracted from the PV system. In this study, a radial basis function neural network (RBF-ANN) based intelligent control method is utilized to map the global operating voltage and non-irradiance operating condition in string and central based MPPT systems. The proposed method has been tested on 10×3 (2.2kW), 15×3 (2.5kW) and 20×3 (3.3kW) of series–parallel PV array configuration under random-shaded and continuous-shaded patterns. The proposed method is compared with the ideal case and conventional method through a simple power–voltage curve of PV arrays. The simulation results show that there are significant increases of about 30–60% of the extracted power in one operating condition when the proposed method is able to shift the operating voltage of modules to their optimum voltages.

Dynamics of Ne‐like populations in the germanium x‐ray laser

Time‐ and two‐dimensional (2‐D) space‐resolved monochromatic imaging is used to study the dynamics of Ne‐like populations in the electron collisionally excited germanium x‐ray laser. Large‐scale variations in the n=3 level population, specifically the upper level of the 2s2p63d‐2s2p63p laser transition, are observed in plasmas created in uniform and nonuniform irradiation conditions, and the degree of homogeneity along the amplification axis is related to the x‐ray gain. The influence of inhomogeneities on the core‐excited 3d‐3p x‐ray lasers is discussed.