Electrical PV Array Reconfiguration Strategy for Energy Extraction Improvement in Grid-Connected PV Systems

This paper applies a dynamical electrical array reconfiguration (EAR) strategy on the photovoltaic (PV) generator of a grid-connected PV system based on a plant-oriented configuration, in order to improve its energy production when the operating conditions of the solar panels are different. The EAR strategy is carried out by inserting a controllable switching matrix between the PV generator and the central inverter, which allows the electrical reconnection of the available PV modules. As a result, the PV system exhibits a self-capacity for real-time adaptation to the PV generator external operating conditions and improves the energy extraction of the system. Experimental results are provided to validate the proposed approach.     

Autonomous robot for cleaning photovoltaic panels in desert zones

In desert zones, a continuous cleaning activity of photovoltaic panels in solar plants is required since the deposition of both airborne dust and sand after a storm can reduce their efficiency up to 80%. Manual cleaning of the photovoltaic panels in dry areas is costly, cannot make use of water and workers must be employed several times in a month, often under extreme environmental conditions. For all these reasons, the research of cleaning solutions performed by autonomous robotic systems are seen beneficial to recover the solar panels efficiency at reasonable costs also nightly. In this respect, this paper presents the implementation of an unmanned low-cost robotic device operating without rails or guides for waterless dust and sand removal from the surface of photovoltaic panels. The robot autonomously moves as a half-track and gently wipes the dust away by means of a couple of independent helical brushes that alternatively rotate, according to a defined combination of the cleaning and motion strategy. Moreover, in real-time the robot detects its spatial position by ultrasonic sensors, regulates both its speed rate and motion direction. The on-board control system, based on an ARDUINO DUE platform, settles the robot travel direction, its speed and which brush must be activated for cleaning. Experimental tests have been performed by fabricating a prototype of the device to assess its effectiveness and reliability in terms of the autonomous motion, dust removal and low power consumption.     

Short-current pulse-based maximum-power-point tracking method formultiple photovoltaic-and-converter module system

This paper proposes a novel maximum-power-point tracking (MPPT) method with a simple algorithm for photovoltaic (PV) power generation systems. The method is based on use of a short-current pulse of the PV to determine an optimum operating current where the maximum output power can be obtained and completely differs from conventional hill-climbing-based methods. In the proposed system, the optimum operating current is instantaneously determined simply by taking a product of the short-current pulse amplitude and a parameter k because the optimum operating current is exactly proportional to the short current under various conditions of illuminance and temperature. Also, the system offers an identification capability of k by means of fast power-versus-current curve scanning, which makes the short-current pulse-based MPPT method adaptive to disturbances such as shades partially covering the PV panels and surface contamination. The above adaptive MPPT algorithm has been introduced into a current-controlled boost chopper and a multiple power converter system composed of PV-and-chopper modules. Various operating characteristics have experimentally been examined on this multiple PV-and-chopper module system from a practical viewpoint and excellent MPPT performance has been confirmed through the tests     

Real-Time Identification of Optimal Operating Points in Photovoltaic Power Systems

Photovoltaic power systems are usually integrated with some specific control algorithms to deliver the maximum possible power. Several maximum power point tracking (MPPT) methods that force the operating point to oscillate have been presented in the past few decades. In the MPPT system, the ideal operation is to determine the maximum power point (MPP) of the photovoltaic (PV) array directly rather than to track it by using the active operation of trial and error, which causes undesirable oscillation around the MPP. Since the output features of a PV cell vary with environment changes in irradiance and temperature from time to time, real-time operation is required to trace the variations of local MPPs in PV power systems. The method of real-time estimation proposed in this paper uses polynomials to demonstrate the power–voltage relationship of PV panels and implements the recursive least-squares method and Newton–Raphson method to identify the voltage of the optimal operating point. The effectiveness of the proposed methods is successfully demonstrated by computer simulations and experimental evaluations of two major types of PV panels, namely: 1) crystalline silicon and 2) copper–indium–diselenide thin film.     

Electronic controlled device for the analysis and design of photovoltaic systems

The characterization and design of photovoltaic systems is a difficult issue due to the variable operation atmospheric conditions. With this aim, simulators and measurement equipments have been proposed. However, most of them do not deal with real atmospheric conditions. This letter proposes an electronic device that first measures the real evolution of the I-V characteristic curves of photovoltaic modules and generators, and then physically emulates in real time these curves to test photovoltaic inverters. The device consists of a dc-dc converter, a microcontroller and a data storage unit. The two operation modes (emulation and measurement) are digitally driven by the microcontroller. The converter current is controlled by means of a variable-hysteresis control loop, whose reference is provided by the microcontroller. In addition, a digital voltage control loop is designed to find out the complete characteristic curves of the photovoltaic generators. A 15-kW prototype is designed and built that can measure three times per second the characteristic curves of up to seven generators and then emulate their electrical behavior to test photovoltaic inverters. With the proposed device, the optimal configuration and performance of photovoltaic modules and generators, as well as the operation of photovoltaic inverters can be thoroughly analyzed under real atmospheric conditions.     

Acceptance sampling plans for photovoltaic modules with two‐sided specification limits

The quality control of photovoltaic modules in terms of the output power to satisfy the technical specification is of great importance for producers as well as consumers and also represents a major issue of certification procedures. Previous work focused on one‐sided specification limits to reject underperforming samples (lots) of photovoltaic modules or solar cells. In the present paper, we generalize the classic acceptance sampling methodology and derive sampling plans on the basis of two‐sided specification limits. Those sampling plans can be constructed for arbitrary output power distributions by making use of flash data tables. For the out‐of‐spec setting, the sampling plans are solutions of rather involved nonlinear equations. Explicit formulas, which resemble known sampling plans, can only be obtained under symmetry assumptions. Further, the solution depends on the ratio of overperforming modules to underperforming modules. We investigate by numerical studies to which extent the required sample size depends on that ratio and the shape of the underlying output power distribution. The application to real examples indicates that in practice, the new approach often results in substantially smaller control samples than classic approaches. Copyright © 2012 John Wiley & Sons, Ltd.     

Methodology and experimental system for measuring and displaying I–V characteristic curves of PV facilities

This paper describes a methodology and the developed system for measuring, capturing, and displaying I–V and P–V characteristic curves of photovoltaic (PV) modules or arrays based on single‐ended primary inductance converters (SEPIC) in parallel connection, operating in interleaved mode. The proposed methodology and the developed system allow the real time capture and displaying of the I–V and P–V curves of a PV panel or array, and show several advantages with regard to classical methods: simple structure, scalability, fast response, versatility, direct display, and low cost. The measuring of the characteristic curves of PV modules includes high speed of response and high fidelity, with low ripple. An experimental prototype based on four SEPIC converters in parallel connection has been implemented to validate the proposed methodology. This new methodology and experimental system has been registered in the Spanish Patent and Trademark Office with the number P200930198. Copyright © 2009 John Wiley & Sons, Ltd.     

A novel maximum power point tracker for PV panels using switching frequency modulation

A novel technique for efficiently extracting maximum power from photovoltaic (PV) panels is presented. The power conversion stage, which is connected between a PV panel and a load or bus, is a SEPIC or Cuk converter or their derived circuits operating in discontinuous inductor-current or capacitor-voltage mode. A method of locating the maximum power point (MPP) is based on injecting a small-signal sinusoidal perturbation into the switching frequency and comparing the AC component and the average value of the panel terminal voltage. Apart from not requiring any sophisticated digital computation of the panel power, the proposed technique does not approximate the panel characteristics and can globally locate the MPP under wide insolation conditions. The tracking capability has been verified experimentally with a 10 W solar panel under a controlled experimental setup. Performances under the steady state and in the large-signal change of the insolation level will are given.     

Volterra-mapping-based behavioral modeling of nonlinear circuits and systems for high frequencies

Presents and validates a discrete-time/frequency-domain approach to the problem of Volterra-series-based behavioral modeling for high-frequency systems. The proposed technique is based on the acquisition of samples of the input/output data, both of which are sampled at the Nyquist rate corresponding to the input signal. The method is capable of identifying the time-/frequency-domain Volterra kernels/transfer functions of arbitrary causal time-invariant weakly nonlinear circuits and systems operating at high frequencies subject to essentially a general random or multitone excitation. The validity and efficiency of the proposed modeling approach has been demonstrated by several examples in high-frequency applications and good agreement has been obtained between results calculated using the proposed model and results measured or simulated with commercial simulation tools.     

Modeling a grid‐connected concentrator photovoltaic system

A six‐parameter formula is proposed for describing the hourly alternating current performance of a grid‐connected, passively cooled concentrator photovoltaic (CPV) system. These system parameters all have physical meanings, and techniques are described for deriving their numerical values. The predictions of the model are compared with the measured output of a Soitec CPV system at Sede Boqer and found to be accurate to approximately ± 5% at all times of the year. The model should also be valid for systems of similar construction operated in different climates from the system studied here, and also for passively cooled CPV systems of different designs provided that suitable numerical values are determined for their system parameters. Another possible use of the model is as a guide for tailoring CPV cell architecture to the particular spectral conditions of the locations in which they will operate. Attention is drawn to the fact that the numerical values of some of the system parameters are found to depend upon the time binning employed for the data. An explanation is given for this phenomenon, which is also found to occur for non‐concentrating photovoltaic panels. Copyright © 2014 John Wiley & Sons, Ltd.     

A New Multilevel Conversion Structure for Grid-Connected PV Applications

A novel scheme for three-phase grid-connected photovoltaic (PV) generation systems is presented in this paper. The scheme is based on two insulated strings of PV panels, each one feeding the dc bus of a standard two-level three-phase voltage-source inverter (VSI). The inverters are connected to the grid by a three-phase transformer having open-end windings on the inverter side. The resulting conversion structure performs as a multilevel power active filter (equivalent to a three-level inverter), doubling the power capability of a single VSI with given voltage and current ratings. The multilevel voltage waveforms are generated by an improved space-vector-modulation algorithm, suitable for the implementation in industrial digital signal processors. An original control method has been introduced to regulate the dc-link voltages of each VSI, according to the voltage reference given by a single maximum power point tracking controller. The proposed regulation system has been verified by numerical simulations and experimental tests with reference to different operating conditions.     

A 1-out-of-N: G system with common-cause failures and critical human errors

A system which has N operating units and r repair facilities with common-cause failures and critical human errors is presented. The system is of 1-out-of-N: G nature. Failure rates are constant and the repair rate is arbitrary. Mathematical formulation is carried out using the supplementary variable technique. Lagrange's method for partial differential equations is employed to solve the governing equations. Various probabilities, system parameters and special cases are discussed.     

Continuous steering-function control of robot carts

Three alternative approaches for eliminating steering discontinuities are presented: changing the steering mechanism, changing the guide-point on the cart, or changing the curves on the path. The first approach requires a steering mechanism that allows the cart to move in any direction without changing its heading. The most common configurations in an automatically guided vehicle are the steered-wheel and differential-drive types. The second approach may be a reasonable choice for differential-drive carts but less so for steered-wheel carts because of their limited maneuverability. For applications where the third approach is preferred, two types of curves providing continuous steering functions for both steered-wheel and differential-drive carts are proposed: Cartesian quintics for lane changes and polar splines for symmetric turns of arbitrary angle. These curves have computationally simple, closed-form expressions that provide continuous curvature and precise matching of the boundary conditions at the line-curve junctions on the paths     

The method of moments for radiation and scattering problems that takes into account cable structures

The method of moments applied for the solution of integral equations arising in problems of scattering and radiation of the electromagnetic field by metal objects is generalized to structures containing cables or closely spaced parallel wires. The interactions between cable conductors are calculated with the help of solutions to plane quasi-static and quasi-stationary problems. It is shown that, with the use of the proposed approach, the arbitrary shape of the cross section of a cable and wires, as well as magnetodielectric coatings and fillings, can be taken into account. Numerical results are compared to analytical solutions and measured data.     

A straightforward method to extract the shunt resistance of photovoltaic cells from current-voltage characteristics of mounted arrays

A straightforward non-invasive method is proposed to accurately evaluate the shunt resistance of an elementary cell of a photovoltaic module connected in an installed string without requiring prior knowledge of the parameters of the intrinsic diodes. The approach relies on the measurement of the current-voltage characteristic of the whole string after intentionally shading the selected cell. Calibrated PSPICE simulations are employed to illustrate the method and test its reliability. As a case study, the shunt resistances of several cells belonging to a series array of 10 commercial panels are determined.     

A method for calculating eigenmodes of shielded waveguides with a complex smoothly varying shape of the cross section

A method is proposed that can be used for calculating eigenmodes of shielded waveguides with an arbitrary smooth dependence of the waveguide parameters on the transverse coordinate. A system of differential equations with boundary conditions is obtained to which the solution of the problem can be reduced. The method is tested with the use of the example of homogeneously and partly filled shielded waveguides. The efficiency of the method is demonstrated through comparison with known results.     

Analysis of oscillator synchronization conditions

The problem of determining the synchronization conditions of an arbitrary oscillator by a small periodic arbitrary waveform signal is considered. It is shown that the problem solution can be found from the existence conditions of small-signal linear system solution. An explicit equation for the oscillator locking range is derived, which can be easily included into a circuit simulation program. A comparison with well-known equations is carried out for a number of special cases. The validity of the suggested approach is verified by the numerical simulation results.     

Novel closed-form Green's function in shielded planar layered media

A new method is proposed for the construction of closed-form Green's function in planar, stratified media between two conducting planes. The new approach does not require the a priori extraction of the guided-wave poles and the quasi-static part from the Green function spectrum. The proposed methodology can be easily applied to arbitrary planar media without any restriction on the number of layers and their thickness. Based on the discrete solution of one-dimensional ordinary differential equations for the spectral-domain expressions of the appropriate vector potential components, the proposed method leads to the simultaneous extraction of all Green's function values associated with a given set of source and observation points. Krylov subspace model order reduction is used to express the generated closed-form Green's function representation in terms of a finite sum involving a small number of Hankel functions. The validity of the proposed methodology and the accuracy of the generated closed-form Green's functions are demonstrated through a series of numerical experiments involving both vertical and horizontal dipoles     

A hybrid modified FA-ANFIS-P&O approach for MPPT in photovoltaic systems under PSCs

ABSTRACT

A modified firefly algorithm (MFO)-based adaptive neuro-fuzzy inference system (ANFIS) combined with the perturbation and observation (P&O) is used in this paper to track the maximum power point (MPP) in photovoltaic systems (PVs). The proposed method identifies and tracks the MPP in two stages. First, according to the irradiance on the solar panels, the ANFIS approximately identifies the MPP. In the second stage, the P&O method starts to act in the tracking cycle and initiates an accurate searching process from that point. The suggested hybrid method covers the problems of commonly-used methods, such as inability in detecting the global MPP under partial shading conditions (PSCs) and trapping in the local optima. Furthermore, the method provides significantly higher speed for the MPP tracking under various irradiance patterns. To prove the above-mentioned claims, the given approach is compared with the P&O method as a common method in the MPPT and particle swarm optimisation (PSO) which operates based on swarm intelligence. Simulation results obtained from MATLAB/Simulink environment show that the proposed method identifies and tracks the MPP under uniform irradiance and PSCs in a very short time of roughly 0.2 s.     

Solar thermoelectric generator for near-earth space applications

The theory, design, fabrication, and testing of flat plate thermoelectric generator panels for near-earth orbits are described. These panels are capable of producing 3 watts/ft²and 15 watts/pound when operating in a near-earth orbit. The potential advantages of these solar energy converters, as compared to photovoltaic cells, are discussed and include higher radiation resistance, improved watts/pound, and lower cost on a per-watt basis.