Determination of magnetic field constant of DC permanent magnet motor powered by photovoltaic for maximum mechanical energy output

The DC permanent magnet motor coupled with centrifugal pump has the better matching when directly powered by photovoltaic (PV) array. The important parameter of DC permanent magnet (DC PM) motor is magnetic field constant. The method for the determination of optimum magnetic field constant of DC PM motor, when powered by PV, has been obtained, and its analysis has been carried out for different magnetic field constants. It has been found that the maximum output is available at the output-energy-weighted average value of magnetic field constant. The parameter, magnetic field constant, should be properly selected during the design of DC PM motor in order to extract the maximum power from PV array.     

Load matching to photovoltaic generators

This paper investigates the suitability of a photovoltaic source to a particular load as regards the degree of load matching in systems that do not employ maximum-power-point-trackers. It is shown that, since the load line is independent of the array characteristics, the array interconnection may be selected to suit the load. The paper identifies two situations in which the system performance can be improved: one through a permanent change in array interconnections from a predominantly series mode to a parallel mode or vice versa; and the other through dynamic array switching from one mode to the other, depending on the solar insolation. Transient analysis of the system due to this array switching has shown that, within a few seconds, the system reaches its new steady-state values.     

Differentiation of multiple maximum power points of partially shaded photovoltaic power generators

Partial shading conditions have a major effect on the electrical characteristics of photovoltaic (PV) power generators. In this paper, the effects of partial shading on maximum power points (MPPs) of a PV power generator have been systematically studied by using Simulink simulation model of a PV power generator composed of 18 series-connected PV modules. It is shown that the local MPPs can be classified into MPPs at low and high voltages based on the MPP operating point of the PV generator. The results also show that based on the MPP current and voltage it is possible to directly know if the MPP at high voltages is a local or a global MPP. The differentiation between local and global MPPs at high voltages is based on the voltage difference between the actual MPP voltage at high voltages and the theoretical MPP voltage under corresponding uniform conditions. This differentiation method was also tested to work correctly by utilizing experimental measurements of the Tampere University of Technology Solar PV Power Station Research Plant. By using this method, it can be identified if the system is operating at a local or a global MPP. This method can further be utilized to develop global MPP tracking algorithms.     

Characterisation of photovoltaic generators

Reliable knowledge on the performance of different photovoltaic generators (as single cells, modules, laminates, shingles, car roofs, etc.) under actual operating conditions is essential for correct product selection and accurate prediction of their electricity production. For this purpose, an outdoor test facility was erected at the Paul Scherrer Institute, PSI. It consists of a sun-tracked sample holder, electronic loads and a PC-based measuring system. Insolation is measured with pyranometers, pyrheliometers and reference cells. Characterisation of a generator under given test conditions means the precise acquisition of its electrical behaviour under varying load. The generator's efficiency and all the relevant electrical parameters are derived on-line from a series of measured current/voltage (I/V) values. I/V-scans at constant insolation and at different generator temperatures enable the temperature coefficients of the efficiency and the electrical parameters to be determined. Thereafter I/V-scans at different insolations (10–1200 W/m²) and air masses (1.1–5) yield (via temperature correction) the insolation dependence of the efficiency at constant temperature. A complete scan takes about 5–15 s. Samples of size varying from 1 by 1 mm up to 1.5 by 1 m can be tested at currents up to 32 A and at voltages up to 120 V. For modelling purposes, the results are represented in the form of correlations, e.g. the efficiency as a function of the operating parameters temperature, insolation and air mass. Results obtained in PSI's test facility were confirmed by the Fraunhofer-Insitut für Solare Energiesysteme, D-79100 Freiburg, Germany. Measurements are presented from some modules and single cells as well as some efficiency correlations. Results are also presented on lamination losses, on PSI's high efficiency cell, on Grätzel cells and watch modules as well as on shading effects and of a small thermophotovoltaic generator.     

A novel maximum power fuzzy logic controller for photovoltaic solar energy systems

The maximum power tracking problem and efficient energy utilization of a stand-alone photovoltaic array (PVA) feeding voltage controlled linear and nonlinear loads is studied. A novel and simple on-line fuzzy logic-based dynamic search, detection and tracking controller is developed to ensure maximum power point (MPP) operation under excursions in solar insolation, ambient temperature and electric load variations. A computer simulation model of the PVA renewable utilization scheme including the effects of temperature and solar irradiation changes was developed and fully simulated. The load voltage is controlled by a DC chopper and kept constant at the required rated voltage. A permanent magnet DC motor (PMDC) driving a fan-type load was connected in parallel to an RL passive load. A speed control scheme is also used for the PMDC motor drive so that the drive can be operated at specified speeds. Different controllers have been employed in the unified PVA scheme to control three separate loads at MPP tracking condition namely voltage at load bus and speed of the PMDC motor. The main objective of the paper is to present a novel enhanced, cost-effective MPP detector (MPPD) and dynamic MPP tracking (MPPT) controller for a hybrid mix of electric loads.     

Matching analysis of photovoltaic powered dc series motors and centrifugal pumps by varing motor constants

An analytical method for the direct coupling between a photovoltaic (PV) generator and a monoblock DC series motor driven centrifugal pump has been developed as a function of the no-flow motor-pump speed w₀ and its working speed w. w₀ is a function of the motor terminal voltage, and w is determined by the value of w₀ and the working water head of the pump. The different parameters of a monoblock DC series motor and a centrifugal pump have been derived as variables of w₀ and w. The optimum matching conditions at the maximum hydraulic efficiency are discussed. The mathematical approach to this study has been verified by experimental results from two different pump systems. The constants of a given motor-pump system are constrained by the requirements and design factors. Without alteration of these constants, better matching can be achieved only by changing the motor constant M₀. Some reported results also compare well with those of this model.     

Nonlinear models for mechanical energy production in imperfect generators driven by thermal or solar energy

In this paper we show how the nonlinear kinetics of energy transfer in propelling fluids and imperfect (non-Carnot) thermal machines can be imbed into the contemporary theory of irreversible energy generators and heat pumps. We quantitatively describe effects of nonlinear heat transfer assuming that heat fluxes are proportional to the difference of temperature in certain power, T^a. We also show that the energy and particle transports can be treated either in a conventional way or as peculiar chemical reactions. In the latter case a recent approach distinguishes in each elementary transfer step two competitive (unidirectional) fluxes and the resulting flux follows as their difference. Nonlinear imperfect systems are investigated in the context of efficiency, heat flux, entropy production and mechanical power, for steady and unsteady operations.     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Test facility in Port Said-Egypt for photovoltaic solar generators

In framework of an applied research project a test facility for evaluating the performance of photovoltaic (PV) solar generators has been implemented at the Faculty of Engineering in Port Said-Egypt. The goals of the project is to perform the different required tests on photovoltaic (PV) solar generators in order to verify the fulfillment of the international standard specifications and to verify the characteristics given by the manufacturer. This will be achieved determining the electrical, the thermal and the mechanical characteristics of the module. This test can be considered to be a preparation for Egyptian PV market helping for propagation and harmonisation of standards. The developed test facility is including the main tests of PV systems, e.g. the electrical output under normal operating conditions and the influence of different environmental factors.     

A maximum power point tracking control strategy with variable weather parameters for photovoltaic systems with DC bus

In photovoltaic (PV) system, the most commonly used DC/DC converter is the basic buck or boost circuit to implement the maximum point power tracking (MPPT) due to their simple structure and low cost while there are some MPPT constraint conditions. By contrast, the conventional buck/boost DC/DC converter without MPPT constraint condition is seldom used because of its high cost or poor performance. To keep the advantages of these three DC/DC converters while overcoming their shortcomings, in this paper, the constraint conditions of capturing the maximum power point (MPP) of PV systems with direct-current (DC) bus are found out. Then, on the basis of this work, a MPPT control strategy with variable weather parameters is proposed. In this strategy, a new buck/boost DC/DC converter is proposed, which not only avoids the MPPT constraint conditions of basic buck or boost DC/DC converter but also overcomes the shortcomings of conventional buck/boost DC/DC converter. Finally, lots of simulated experiments verify the accuracy of MPPT constraint conditions, test the feasibility and availability of proposed MPPT control strategy, analyze the MPPT performance of proposed PV system and compare the output transient-state performance with conventional perturb and observe (P&O) method.     

Simulating the dust effect on the energy performance of photovoltaic generators based on experimental measurements

One of the least analyzed side effects of atmospheric air pollution is the degradation of PV-panels’ performance due to the deposition of solid particles varying in composition, size and type. In the current study, the experimental data concerning the effect of three representative air pollutants (i.e. red soil, limestone and carbonaceous fly-ash particles) on the energy performance of PV installations are analyzed. According to the results obtained, a considerable reduction of PVs’ energy performance is recorded, depending strongly on particles’ composition and source. Subsequently, a theoretical model has been developed in order to be used as an analytical tool for obtaining reliable results concerning the expected effect of regional air pollution on PVs’ performance. Furthermore, experimental results concerning the dust effect on PVs’ energy yield in an aggravated - from air pollution - urban environment are used to validate the proposed theoretical model.     

High-accuracy maximum power point estimation for photovoltaic arrays

Quantitative information regarding the maximum power point (MPP) of photovoltaic (PV) arrays is crucial for determining and controlling their operation, yet it is difficult to obtain such information through direct measurements. PV arrays exhibit an extremely nonlinear current-voltage (I-V) characteristic that varies with many complex factors related to the individual cells, which makes it difficult to ensure an optimal use of the available solar energy and to achieve maximum power output in real time. Finding ways to obtain the maximum power output in real time under all possible system conditions are indispensable to the development of feasible PV generation systems. The conventional methods for tracking the MPP of PV arrays suffer from a serious problem that the MPP cannot be quickly acquired. Based on the p-n junction semiconductor theory, we develop a prediction method for directly estimating the MPP for power tracking in PV arrays. The proposed method is a new and simple approach with a low calculation burden that takes the resistance effect of the solar cells into consideration. The MPP of PV arrays can be directly determined from an irradiated I-V characteristic curve. The performance of the proposed method is evaluated by examining the characteristics of the MPP of PV arrays depending on both the temperature and irradiation intensity, and the results are discussed in detail. Such performance is also tested using the field data. The experimental results demonstrate that the proposed method helps in the optimization of the MPP control model in PV arrays.     

Step-up maximum power point tracker for photovoltaic arrays

This paper discusses a new maximum power point tracker (MPPT), which has been devised and tested at the laboratory. This MPPT is a high-frequency set-up dc-to-dc power conditioning unit. Simple and inexpensive analog circuitry is used to continually maximize the true PV array output power rather than maximizing the current or voltage at either the PV array or load. The control circuit is designed such that the actual current and voltage are sensed directly from the PV array. These two signals are then multiplied by a single-chip multiplier.The multiplier output charges or discharges two separate RC circuits of different time constants. These two RC signals are then mixed to set the duty cycle of a pulse width modulated signal to continually track the array maximum power point.This MPPT is simple and inexpensive; and it continuously tracks the true PV array maximum power point regardless of the load type.     

A maximum power tracking algorithm based on photovoltaic current control for matching loads to a photovoltaic generator

In this paper, a novel maximum power point tracking (MPPT) approach is studied. It is based on the photovoltaic (PV) current control. The last one is estimated using an estimation algorithm. It is established based on the Newton Raphson optimization algorithm. Digital simulation results for a resistive load are presented to highlight the improvement in performances of the presented MPPT approach.     

Sizing optimisation of stand-alone photovoltaic generators for irrigation water pumping systems

This paper mainly presents an efficient non-conventional direct method for sizing optimisation of stand-alone photovoltaic (PV) generators for supplying AC-motor-based irrigation pumping systems. The efficiencies of various elements comprising a PV pumping system and the effects of PV-array tilt are taken into account. The strong impact of the tilt angle on the optimal sizing of a PV generator is demonstrated. Extensive analysis of the meteorological conditions of the study site is performed. An appropriate solar correlation model for the design site is determined. The optimality of the determined capacity and tilt angle for a PV generator is evaluated by calculating several optimality indicators. The proposed method is compared with the Kenna and Gillett method and the RETScreen method for suggesting the nominal power for PV generators. The results show the capability and accuracy of the proposed method in optimally sizing stand-alone PV generators for irrigation water pumping systems.     

通用型水泵电机的光伏驱动系统研究

目前光伏水泵的推广面临两个方面的障碍,一方面是应用较多的专用型光伏机泵成本较高;另一方面利用通用变频器驱动通用机泵时光伏利用率低。为了克服这些不足,设计了一种针对通用型水泵电机的光伏驱动系统。系统基于数字信号控制器dsPIC30F2010和IPM智能功率模块,实现了安全稳定运行、真正的最大功率跟踪（TMPPT）及模块化结构。分析了系统的硬件结构,探讨了系统的控制思想及实现,并用实验结果证明了设计的正确性。     

A photovoltaic utilization system with bang–bang self-adjusting maximum energy tracking controller

The paper presents an error driven controller for maximum energy utilization of photovoltaic PV renewable energy interface schemes. The error driven comprises of regulation loops ensuring on-line dynamic tracking of the maximum power point under different variations in solar insulation levels or sudden mechanical load excursions. The bang–bang regulator limiter block is self-adjusting as it is driven by the error excursion vector magnitude. This ensures that the control signal is modulated in magnitude by the distance of error deviation in the error hyper plane. The paper details a digital simulation MATLAB/SIMULINK model of a PV−PMDC motor utilization system driving a ventilation, pumping or air-conditioning mechanical load. © 1998 John Wiley & Sons, Ltd.     

Polymer-based nanopiezoelectric generators for energy harvesting applications

Abstract

Energy harvesting from ambient vibrations originating from sources such as moving parts of machines, fluid flow and even body movement, has enormous potential for small power applications, such as wireless sensors, flexible, portable and wearable electronics, and bio-medical implants, to name a few. Nanoscale piezoelectric energy harvesters, also known as nanogenerators (NGs), can directly convert small scale ambient vibrations into electrical energy. Scavenging power from ubiquitous vibrations in this way offers an attractive route to provide power to small devices, which would otherwise require direct or indirect connection to electrical power infrastructure. Ceramics such as lead zirconium titanate and semiconductors such as zinc oxide are the most widely used piezoelectric energy harvesting materials. This review focuses on a different class of piezoelectric materials, namely, ferroelectric polymers, such as polyvinlyidene fluoride (PVDF) and its copolymers. These are potentially superior energy harvesting materials as they are flexible, robust, lightweight, easy and cheap to fabricate, as well as being lead free and biocompatible. We review some of the theoretical and experimental aspects of piezoelectric energy recovery using Polymer-based NGs with a novel emphasis on coupling to mechanical resonance, which is relevant for efficient energy harvesting from typically low frequency (<1 kHz) ambient vibrations. The realisation of highly efficient and low cost piezoelectric polymer NGs with reliable energy harvesting performance could lead to wide ranging energy solutions for the next generation of autonomous electronic and wireless devices.     

Cost predictions for photovoltaic energy sources

A preliminary assessment of the solar cell cost prediction art has been made, both in terms of a review and analysis of the prior literature and through an extension of these prior studies. The primary purpose of this study is to establish a basis for judging the relative credibility of the existing cost estimates.The initial step in this evaluation is to develop a self-consistent system of “reaonable” assumptions concerning the future market environment of solar cell energy sources. The second step is to establish the key assumptions which dominate the cost estimates obtained in prior studies. The results from these first two steps form the basis for judging the relative credibility of the existing cost predictions.Finally, an alternative set of cost estimates is generated. These alternative cost predictions are made for single-crystal Si cells (Czochralski vs “ribbon” growth), current technology Cu₂S---CdS cells, and a “generalized” thin-film photovoltaic device.