Optimum load matching in direct-coupled photovoltaic powersystems-application to resistive loads

The load matching factor is used as a measure for the quality of load matching to a photovoltaic (PV) array. An optimization approach is used to solve the load matching problem with the objective of maximizing the load matching factor, and consequently the PV output energy. This approach is then applied to resistive loads (with and without an internal EMF) connected to the array. Results show that optimum matching can be achieved by carefully selecting the array parameters with respect to the load parameters. The temperature of the array has little effect on the optimum matching factor. However, the optimum matching parameters are greatly affected by the array temperature. A maximum power tracker may not be achieved     

Optimum matching of ohmic loads to the photovoltaic array

Optimum matching of loads to the photovoltaic (PV) generator is most desirable for more accurate sizing, higher system performance and maximum utilization of the costly solar array generator. The quality of load matching depends on the PV array characteristics, the load characteristics, and the insolation profile. A matching factor is defined as the ratio of the load energy to the array maximum energy over a one day period. Optimum matching is achieved by determining the optimal array parameters with respect to the load parameters. Optimization is done using direct-search techniques. Results show that the theoretical optimum matching factor for an ohmic load is 94.34%. For an electrolytic load the matching factor could reach 99.83%. A maximum power tracker can be eliminated if optimum matching is achieved.     

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.     

Optimum turbine-site matching

This paper presents a new formulation for the turbine-site matching problem, based on wind speed characteristics at any site, the power performance curve parameters of any pitch-regulated wind turbine, as well as turbine size and tower height. Wind speed at any site is characterized by the 2-parameter Weibull distribution function and the value of ground friction coefficient (α). The power performance curve is characterized by the cut-in, rated, and cut-out speeds and the rated power. The new Turbine-Site Matching Index (TSMI) is derived based on a generic formulation for Capacity Factor (CF), which includes the effect of turbine tower height (h). Using the CF as a basis for turbine-site matching produces results that are biased towards higher towers with no considerations for the associated costs. The proposed TSMI includes the effects of turbine size and tower height on the Initial Capital Cost (ICC) of wind turbines. The effectiveness and the applicability of the proposed TSMI are illustrated using five case studies. In general, for each turbine, there exists an optimal tower height, at which the value of the TSMI is at its maximum. The results reveal that higher tower heights are not always desirable for optimality.     

Optimum windmill-site matching

A methodology for the selection of the optimum windmill for a specific site is developed. The selection is based on finding the capacity factors of the available windmills. This is done by using long-term wind speed data recorded at different hours of the day for many years. These data are then used to generate mean wind speeds for a typical day in a month. Probability density functions for the mean wind speeds for the different hours of the day are generated with the manufacturer's specifications on the windmills used to calculate the capacity factors for the windmills. The windmill with the highest average capacity factor for the specific site is the optimum one and should be recommended     

Analysis of optimum matching of a DC series motor driven centrifugal pump to a photovoltaic generator

Direct coupling between a photovoltaic (PV) generator and a monoblock DC series motor connected with ventilator load torque centrifugal pump has been analyzed theoretically as a function of the no flow motor-pump speed (w₀) and the water head of the pump. The value of w₀ is directly related with motor terminal voltage which has been derived. The condition of the maximum motor-pump efficiency has been deduced mathematically in terms of the speed-torque constant K₁ at a given w₀ for different water heads. The variation of w₀ and perfectly matched motor constant (M₀) have been calculated at various solar insolation and different water heads. From these theoretical studies, the optimum matching condition has been suggested according to the requirements. One optimally matched monoblock DC series motor and centrifugal pump, of 125 W, was chosen for study. The calculated coupling efficiencies such as electrical energy, mechanical energy, and hydraulic energy of the pump, have been discussed. Some of these results are also compared to information available in the literature.     

风力发电机风轮与发电机匹配特性的试验研究

为了提高风力发电机的输出性能,针对离网小型风力机的风轮能量转换系统和发电机系统的性能进行了研究。通过对两副风轮、两台发电机进行交叉组合试验,分别采集了尖速比为3～8、风速为7～13 m/s时风力发电机的功率特性,同时还采集了发电机在不同工况下的温度场、扭矩、功率等参数,选出输出特性较好的发电机和风轮,然后将其组合,对其输出特性进行研究,并测试分析了整机的振动特性。寻找影响发电机系统性能及发电机与风轮系统匹配的相关规律及有机结合点。研究结果表明,风轮和发电机组合后的整体性能不是由单一因素决定的,而是由叶片翼型及安装方式、发电机的结构和技术参数等因素共同作用产生的综合效果,发电机的影响尤为明显。     

Optimum sizing of battery-integrated diesel generator for remote electrification through design-space approach

Battery integrated diesel generation is one of the options for decentralized power production. They are particularly suitable for loads with significant variation in the daily demand. A methodology for the optimum sizing of integrated system involving diesel generator and battery bank for an isolated electrical power generation is proposed in this paper. The proposed methodology is based on the design-space approach involving a time series simulation of the entire system. Based on the proposed approach, for a given load demand, characteristics of the diesel generator and battery bank, a sizing curve is identified on the diesel generator rating vs. storage capacity diagram. The sizing curve helps in identifying all possible feasible system configurations or the design space. Based on the minimum capital cost and the minimum operating cost of the system, the Pareto optimum curve is identified on the system-sizing curve. Optimum system configuration is identified based on the minimum cost of energy through optimal dispatch strategy. Two operating strategies, involving continuous and intermittent operation of the diesel generator are studied and compared. Effect of the load profile on the system sizing is also presented in this paper.     

A novel excitation scheme for a stand-alone three-phase induction generator supplying single-phase loads

This paper presents the operating principle and steady-state analysis of a novel excitation scheme for a stand-alone three-phase induction generator that supplies single-phase loads. The phase windings and excitation capacitances are arranged in the form of the Smith connection and the excitation scheme is referred to as the SMSEIG. In addition to providing the reactive power for self-excitation, the capacitances also act as phase balancers. With this novel excitation scheme, isolated single-phase loads can be supplied with good phase balance in the induction machine, resulting in high efficiency, large power output, and quiet machine operation. Performance analysis is based on the method of symmetrical components, from which the input impedance of the generator can be determined. Numerical solution of a simplified equivalent circuit for the machine variables, namely the excitation frequency and magnetizing reactance, enables the generator performance to be evaluated for any load and speed. With the aid of a phasor diagram, the conditions for achieving perfect phase balance are deduced and a method to compute the capacitances required is developed. Experimental investigations on a 2.2-kW induction machine confirm the feasibility of the SMSEIG.     

Design optimization and site matching of direct-drive permanent magnet wind power generator systems

This paper investigates the possible site matching of the direct-drive wind turbine concepts based on the electromagnetic design optimization of permanent magnet (PM) generator systems. Firstly, the analytical models of a three-phase radial-flux PM generator with a back-to-back power converter are presented. The optimum design models of direct-drive PM wind generation system are developed with an improved genetic algorithm, and a 500-kW direct-drive PM generator for the minimal generator active material cost is compared to demonstrate the effectiveness of the design optimization. Forty-five PM generator systems, the combinations of five rated rotor speeds in the range of 10–30 rpm and nine power ratings from 100 kW to 10 MW, are optimally designed, respectively. The optimum results are compared graphically in terms of the generator design indexes. Next, according to the design principle of the maximum wind energy capture, the rotor diameter and the rated wind speed of a direct-drive wind turbine with the optimum PM generator are determined. The annual energy output (AEO) is also presented using the Weibull density function. Finally, the maximum AEO per cost (AEOPC) of the optimized wind generator systems is evaluated at eight potential sites with annual mean wind speeds in the range of 3–10 m/s, respectively. These results have shown the suitable designs for the optimum site matching of the investigated PM generator systems.     

含不平衡负载的微电网中三相微源逆变器的VSG控制策略

在离网模式下,微电网中虚拟同步发电机的输出电压易受不平衡负载影响。针对此问题,文章基于一阶全通滤波器(All-Pass Filter,APF)的电压电流正、负序分离方法,利用正序功率和正序电流建立了改进VSG控制模型,改善了VSG输出电压参考。采用比例积分(Proportional Integral,PI)+准比例谐振(Quasi Proportional Resonant,QPR)电压调节器对VSG输出负序电压分量进行控制,论证了PI+QPR调节器抑制负序电压分量的优良性能。最后,仿真结果验证了该控制策略的有效性,该方法有效地改善了三相微源逆变器输出电压的对称性。     

A maximum power tracking algorithm based on Impp = f(Pmax) function for matching passive and active loads to a photovoltaic generator

In this paper, a method that forces a photovoltaic generator (PVG) to operate at its maximum power point under variable load and insolation conditions is developed. The method is based on closed loop current control, in which the reference current is determined from the fitted function of I_mpp versus P_max, points of a particular PVG. A simplified computer model of the PVG is given and computer simulations for demonstrating the effectiveness of the proposed algorithm are presented. The method has also been applied using a PC with IO interface card in the laboratory. From the results of the simulations and experimental studies, it is concluded that the proposed approach can be used as a robust and fast acting maximum power point tracker.     

Probabilistic load flow with detailed wind generator models considering correlated wind generation and correlated loads

The enhancement in the penetration of intermittent generation necessitates the need to include uncertain behaviour in the conventional power flow programs. In this paper, four different wind generation models have been incorporated in probabilistic load flow for calculating the probability distribution of the reactive power consumed by the wind generators for three different scenarios; i) uncorrelated wind and uncorrelated loads ii) uncorrelated wind and correlated loads and iii) correlated wind and correlated loads The above mentioned scenarios have been implemented in probabilistic load flow using point estimate method in the IEEE-118 bus test system and accuracy of the results have been validated by comparing these results with those obtained by Monte Carlo simulation studies.     

Unbalanced voltage faults: the impact on structural loads of doubly fed asynchronous generator wind turbines

This paper investigates the impact that unbalanced voltage faults have on wind turbine structural loads. In such cases, electromagnetic torque oscillations occur at two times the supply voltage frequency. The objectives of this work are to quantify wind turbine structural loads induced by unbalanced voltage faults relative to those during normal operation; and to evaluate the potential for reducing structural loads with the control of the generator. The method applied is integrated dynamic analysis. Namely, dynamic analysis with models that consider the most important aeroelastic, electrical, and control dynamics in an integrated simulation environment based on an aeroelastic code (HAWC2) and software for control design (Matlab/Simulink). In the present analysis, 1 Hz equivalent loads are used to compare fatigue loads, whereas maximum–minimum values are used to compare extreme loads. A control concept based on resonant filters demonstrates reduction of the structural loads (shaft torsion and tower top side‐to‐side moment) induced by an unbalanced voltage fault.Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental investigation and modeling of a direct-coupled PV/T air collector

Photovoltaic/thermal (PV/T) systems refer to the integration of photovoltaic and solar thermal technologies into one single system, in that both useful heat energy and electricity are produced. The impetus of this paper is to model a direct-coupled PV/T air collector which is designed, built, and tested at a geographic location of Kerman, Iran. In this system, a thin aluminum sheet suspended at the middle of air channel is used to increase the heat exchange surface and consequently improve heat extraction from PV panels. This PV/T system is tested in natural convection and forced convection (with two, four and eight fans operating) and its unsteady results are presented in with and without glass cover cases. A theoretical model is developed and validated against experimental data, where good agreement between the measured values and those calculated by the simulation model were achieved. Comparisons are made between electrical performance of the different mode of operations and it is concluded that there is an optimum number of fans for achieving maximum electrical efficiency. Also, results show that setting glass cover on photovoltaic panels leads to an increase in thermal efficiency and decrease in electrical efficiency of the system.     

贴在墙上的发电机

目前，石油价格节节上升，使得像美国、日本、中国等石油进口大国经济受到一定的影响。因此，寻找替代品成了这些国家的一项国策。在美国，太阳能发电、潮汐发电、垃圾发电、甚至利用火鸡的废料发电等一一上马，并且取得了一定的成就。其后，五花八门的新能源研究齐头并进，光伏发电就是很受人们推崇的清洁能源。那么，“发电机”是怎么贴到墙上的呢？     

Optimal site matching of wind turbine generator: Case study of the Gulf of Suez region in Egypt

During the last few years, Egypt has emerged as the leader of wind power in the Middle East and Africa. In the Gulf of Suez region, a continuously expanding large-scale grid-connected wind farm is available at Zafarana site. The Gulf of EL-Zayt site in the Gulf of Suez region is now under extensive studies related to wind power projects such as feasibility and bird migration studies. Therefore, the Gulf of Suez region is considered in this paper for optimal site matching of wind turbine generator (WTG). This paper treats the problem of site matching of WTG through improved formulation of the capacity factor. Such factor is estimated based on Weibull PDF and an accurate model for the WTG output-power-curve. Ornithological, martial, and other limitations placed on WTG hub heights in the Gulf of Suez region in Egypt are taken into account. In addition, a MATLAB based program is created to implement the presented technique of optimal site matching of WTG. Based on turbine-performance-index (TPI) maximization, optimal output-power-curve and optimal commercial WTG are determined for each candidate site in the Gulf of Suez region. Long-term performance measurements at Zafarana wind farms in comparison with the results are used to validate the presented technique and the optimality of the results.     

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.     

A review on electromechanical equipment applicable to small hydropower plants

Small hydropower (SHP) projects are considered by the developers as these provide renewable source of energy and are environment friendly. The basic cost components of SHP scheme are broadly classified as civil works and electromechanical equipment. The most important components under the electromechanical equipment are turbine and generator. In the present paper, an attempt has been made to review the different types of technological models and transfer function developed to evaluate the performance of the electromechanical equipment of SHP projects. A review on the different types of control strategies developed by earlier investigators has also been presented. The present review attempts to cover the different types of design and analysis made on different types of turbines, generator and control equipment of SHP. Copyright © 2012 John Wiley & Sons, Ltd.     

Orthotropic pressure vessels subject to local loads

Differential equations for unsymmetrical loading of simply supported orthotropic circular cylindrical shell are obtained in terms of displacement components. Then displacement components are expressed in the form of double trigonometric Fourier series that satisfies the boundary conditions at the end. Uniformly distributed load on rectangular areas is considered, which is again expressed in terms of double trigonometric Fourier series. Expressions are obtained for displacement components, stress-resultants and stress-couples. Numerical results are obtained and plotted for a particular case.