Optimal Su-Do-Ku based interconnection scheme for increased power output from PV array under partial shading conditions

Partial shading is a common phenomenon in PV arrays. They drastically reduce the power output because of mismatch losses, which are reliant on the shape of the shade as well as the locations of shaded panels in the array. The power output can be improved by distributing the shade over various rows to maximize the current entering the node. A Su-Do-Ku configuration can be used to rearrange the physical locations of the PV modules in a total cross tied PV array with the electrical connections left unchanged. However, this arrangement increases the length of the wire required to interconnect the panels thus increasing the line losses. In this paper, an improved Su-Do-Ku arrangement that reduces the length of the wire required for the connection is proposed. The system is designed and simulated in a Matlab/Simulink environment for various shading patterns and the efficacies of various arrangements are compared. The results prove that the power output is higher in the proposed improved Su-Do-Ku reconfiguration technique compared to the earlier proposed Su-Do-Ku technique.     

Performance enhancement of partially shaded solar PV array using novel shade dispersion technique

Solar photo voltaic array (SPVA) generates a smaller amount of power than the standard rating of the panel due to the partial shading effect. Since the modules of the arrays receive different solar irradiations, the P-V characteristics of photovoltaic (PV) arrays contain multiple peaks or local peaks. This paper presents an innovative method (magic square) in order to increase the generated power by configuring the modules of a shaded photovoltaic array. In this approach, the physical location of the modules in the total cross tied (TCT) connected in the solar PV array is rearranged based on the magic square arrangement pattern. This connection is done without altering any electrical configurations of the modules in the PV array. This method can distribute the shading effect over the entire PVarray, without concentrating on any row of modules and can achieve global peaks. For different types of shading patterns, the output power of the solar PV array with the proposed magic square configuration is compared with the traditional configurations and the performance is calculated. This paper presents a new reconfiguration technique for solar PV arrays, which increases the PV power under different shading conditions. The proposed technique facilitates the distribution of the effect of shading over the entire array, thereby, reducing the mismatch losses caused by partial shading. The theoretical calculations are tested through simulations in Matlab/ Simulink to validate the results. A comparison of power loss for different types of topologies under different types of shading patterns for a 4×4 array is also explained.     

Forecasting photovoltaic array power production subject to mismatch losses

The development of photovoltaic (PV) energy throughout the world this last decade has brought to light the presence of module mismatch losses in most PV applications. Such power losses, mainly occasioned by partial shading of arrays and differences in PV modules, can be reduced by changing module interconnections of a solar array. This paper presents a novel method to forecast existing PV array production in diverse environmental conditions. In this approach, field measurement data is used to identify module parameters once and for all. The proposed method simulates PV arrays with adaptable module interconnection schemes in order to reduce mismatch losses. The model has been validated by experimental results taken on a 2.2 kW_p plant, with three different interconnection schemes, which show reliable power production forecast precision in both partially shaded and normal operating conditions. Field measurements show interest in using alternative plant configurations in PV systems for decreasing module mismatch losses.     

Self-shading losses of fixed free-standing PV arrays

The energy yield of a photovoltaic (PV) system with fixed free-standing PV arrays is affected also by the self-shading effects. The rows of PV modules in arrays may partially shade the PV modules in the rows behind. In this paper the effects of the row distance on the PV system’s energy yield are evaluated. The estimation of the self-shading losses by the irradiation losses simply overestimates the losses; therefore we developed a simulation model to simulate the real energy loss due to shading of the preceding row in a PV system. The model demonstrates that the self-shading energy losses are at commonly used distances between rows from 20 to 40% lower than the irradiation losses at the modules’ bottom considering the shading conditions. The self-shading energy loss is studied in the case of Ljubljana, Slovenia which may refer to the whole Central Europe. To estimate the self-shading losses a technology-and with parameter modifications also location-independent empirical equation based on module-to-cell width ratio was derived and validated.     

Reconfiguration solution for shaded PV panels using switching control

This paper applies a new dynamical electrical array reconfiguration strategy on photovoltaic (PV) panels arrangement based on the connection of all PV panels on two parallel groups to reach the 24 V requested by the considered load and providing a maximum output current by connecting in series the two groups. If one of the PV panels or more are shaded, dusty or faulty the connection of the others in the same group will be automatically modified to maintain the requested load output voltage. This dynamical reconfiguration allows also limiting the lost power, due to the incriminate panel, by switching off this panels and reconfiguration the topology. As a result, a real time adaptation of a switch matrix allows a self-ability to maintain a constant load voltage. Moreover, a minimum number of PV panels are switched off by isolating the effect of unhealthy panels. In addition, the proposed solution can also be applied for identifying and locating the shaded, dusty and faulty panel. Experimental setup has been built and the results validate the proposed method.     

Analysis of spatial fixed PV arrays configurations to maximize energy harvesting in BIPV applications

This paper presents a new approach for efficient utilization of building integrated photovoltaic (BIPV) systems under partial shading conditions in urban areas. The aim of this study is to find out the best electrical configuration by analyzing annual energy generation of the same BIPV system, in terms of nominal power, without changing physical locations of the PV modules in the PV arrays. For this purpose, the spatial structure of the PV system including the PV modules and the surrounding obstacles is taken into account on the basis of virtual reality environment. In this study, chimneys which are located on the residential roof-top area are considered to create the effect of shading over the PV array. The locations of PV modules are kept stationary, which is the main point of this paper, while comparing the performances of the configurations with the same surrounding obstacles that causes partial shading conditions. The same spatial structure with twelve distinct PV array configurations is considered. The same settling conditions on the roof-top area allow fair comparisons between PV array configurations. The payback time analysis is also performed with considering local and global maximum power points (MPPs) of PV arrays by comparing the annual energy yield of the different configurations.     

Determination of energy output losses due to shading of building-integrated photovoltaic arrays using a raytracing technique

In this contribution a simulation procedure is described which was developed as a working tool to calculate the energy output of building-integrated photovoltaic (PV) arrays experiencing shading or reflection effects. A three-quadrant solar cell model incorporating the reverse bias characteristics and breakdown voltage is verified by current-voltage (I–V) measurements performed on commercially manufactured mc-Si solar cells under controlled laboratory conditions. For the simulations, a point matrix giving the irradiation distribution over the PV array is calculated for each hour using a raytracing technique. With a raytracing technique, shading of both beam and diffuse irradiation as well as primary and secondary reflections can be modelled. The results of two cases studies simulated using this technique are presented and analysed. In conclusion, general guidelines based on the simulation results are drawn up. These guidelines aim to assist architects and engineers in planning an optimized layout strategy of building-integrated PV arrays to reduce energy losses caused by shading.     

Calculation of the PV modules angular losses under field conditions by means of an analytical model

Photovoltaic (PV) modules in real operation present angular losses in reference to their behaviour in standard test conditions, due to the angle of incidence of the incident radiation and the surface soil. Although these losses are not always negligible, they are commonly not taken into account when correcting the electrical characteristics of the PV module or estimating the energy production of PV systems. The main reason of this approximation is the lack of easy-to-use mathematical expressions for the angular losses calculation. This paper analyses these losses on PV modules and presents an analytical model based on theoretical and experimental results. The proposed model fits monocrystalline as well as polycrystalline and amorphous silicon PV modules, and contemplates the existence of superficial dust. With it angular losses integrated over time periods of interest can be easily calculated. Monthly and annual losses have been calculated for 10 different European sites, having diverse climates and latitudes (ranging from 32° to 52°), and considering different module tilt angles.     

A virtual reality study of surrounding obstacles on BIPV systems for estimation of long-term performance of partially shaded PV arrays

This work presents a new analytical method to evaluate the efficiency of PV systems working in partial shading conditions by taking into account the effect of surrounding obstacles. A mathematical procedure to determine the shadowed area on PV modules, depending on the location of the PV system and obstacles nearby the array has been implemented. This methodology allows the study of the power losses present in the PV systems due to partial shading conditions as well as its effect on the evolution of the maximum power point of the array. The application of this methodology on the behavior of three PV systems located in different cities of Turkey, such as Istanbul, Izmir, and Antalya, working under the same conditions of obstacle surrounding, along a year is presented.     

A grid-connected photovoltaic power conversion system with single-phase multilevel inverter

This paper presents a grid-connected photovoltaic (PV) power conversion system based on a single-phase multilevel inverter. The proposed system fundamentally consists of PV arrays and a single-phase multilevel inverter structure. First, configuration and structural parts of the PV assisted inverter system are introduced in detail. To produce reference output voltage waves, a simple switching strategy based on calculating switching angles is improved. By calculated switching angles, the reference signal is produced as a multilevel shaped output voltage wave. The control algorithm and operational principles of the proposed system are explained. Operating PV arrays in the same load condition is a considerable point; therefore a simulation study is performed to arrange the PV arrays. After determining the number and connection types of the PV arrays, the system is configured through the arrangement of the PV arrays. The validity of the proposed system is verified through simulations and experimental study. The results demonstrate that the system can achieve lower total harmonic distortion (THD) on the output voltage and load current, and it is capable of operating synchronous and transferring power values having different characteristic to the grid. Hence, it is suitable to use the proposed configuration as a PV power conversion system in various applications.     

Maximum power tracking in solar cell arrays using time-based reconfiguration

Directly harnessed solar power is an attractive primary energy source for integration into fully wire-free, self-sufficient, portable electronic devices. Maximum power (MPP) tracking of photovoltaic (PV) cells is an essential part of PV energy harvesting and several methods are available to track MPP efficiently. With more than one cell, power-balancing is also a significant concern and global MPP tracking, parallel connection of PV cells, and active array reconfiguration are all techniques designed to address this issue. This work shrinks array reconfiguration from two-dimensional arrays of PV cells to a single string of PV cells, which are particularly relevant to portable systems. Each string element has individual MPP tracking and power balancing at low circuit complexity using a modular, time-domain array-reconfiguration (TDAR) approach. Both, a discrete control loop that demonstrates the concept and a 150 μW microchip that implements TDAR for three PV cells were developed. The energy harvesting efficiency of the TDAR approach is more than 80% improved compared to static (non-reconfigurable) strings of PV cells. While other array reconfiguration approaches can offer comparable improvements in efficiency, the reduced complexity of the TDAR approach makes it the only scalable approach that can be practically applied to array reconfiguration in portable systems.     

基于并联光伏组件外特性的最大功率点跟踪方法

当阴影条件变化时,并联光伏组件的全局最大功率点(MPP)会随之改变.为了实现太阳能发电最大化,要求最大功率点跟踪(MPPT)方法始终能实时而准确地锁定住并联光伏组件的全局MPP.不同阴影条件下并联光伏组件会呈现不同的外特性特征,如多阶梯的电流电压特性以及多峰值的功率电压特性.基于此现象,该文提出一种基于并联光伏组件外特...     

Effects of mismatch losses in photovoltaic arrays

Experimental and modeling results on the effects of mismatch losses in photovoltaic arrays are presented. Field tests conducted on each of the 192 modules are used to describe the variation in the properties of production run photovoltaic modules. Module specific estimates of a five-parameter module model are obtained by nonlinear regression. Mathematical models of four-module parallel string and series block photovoltaic array performance based on the five-parameter module model are developed and used to evaluate the variation in maximum output power and mismatch loss of arrays with random module orderings. Module maximum output power averaged 14% below the nameplate rating and exhibited a coefficient of variation of 2.1%. Mismatch losses were very small, never exceeding 0.53%. No differences between parallel string and series block arrays in array maximum output power were observed.     

一种阴影情况下光伏组件输出特性的计算方法

提出了一种计算阴影遮挡情况下组件输出特性的方法。该方法首先根据流经组件的电流对被遮挡电池及其所在电池串的输出特性进行分析,在此基础上对旁路二极管的伏安特性进行理论分析,进而判定旁路二极管导通状态,从而计算出光伏组件在阴影遮挡情况下的多峰特性。经试验验证,此种方法可精确地模拟复杂遮挡情况下光伏组件的输出特性,对于各种阴影遮挡情况下的峰值点的最大误差在3%以内。该方法较传统的失配情况下基于一个电池单元并联一个保护旁路二极管的计算方法更符合实际,具有较强的实用价值。     

Evaluation of electric energy performance by democratic module PV system field test

A systematic investigation has been made on annual accumulated generated PV power from different solar arrays consisting of three kinds of silicon-based solar cells. To clarify seasonal output power variations with temperature in c-Si and a-Si cells might be an important issue for the operations of PV system. It has been shown from the results that electric output power from a-Si array in summer is 20% larger than that from c-Si. On the other hand, in winter, this scene should be reverted. However, output power from c-Si array is only 5% larger than that from a-Si. The analyzed data also shows that annual accumulated electric power generated from a-Si array corresponds to 90% of its nominal efficiency in the year. While in case of c-Si array, this ratio is about 84%.     

Reliable and efficient approach for mitigating the shading effect on photovoltaic module based on Modified Artificial Bee Colony algorithm

The operation and performance of a photovoltaic system (PV) are affected by some factors such as; solar radiation, ambient temperature, PV array configuration and shadow which may be either completely or partially. The partially shadow is caused by clouds, trees due to wind, neighboring buildings and utilities. The shadow effect causes the multiple local maximum power points in the PV module voltage-power characteristics and only one Global Maximum Power Point (GMPP); additionally the shadowing causes high power loss in the shaded cells and produces hot spot. In this paper a new optimization approach based on proposed Modified Artificial Bee Colony (MABC) algorithm is used to solve a proposed constrained objective function of PV module power loss and mitigate the shading effect. The proposed MABC is compared with GA, PSO and ABC. The obtained results proved that the MABC is the most efficient algorithm in solving the objective function that mitigating the power loss in the PV module under partially shading effect.     

大型地面光伏电站中光伏方阵容量的优化设计

随着光伏组件光电转换效率的提高,以及逆变器单机功率的增大,大型地面光伏电站中光伏方阵容量也从1 MW、1.6 MW、2.5 MW逐渐增大到3.125 MW。以新疆维吾尔自治区吐鲁番地区的气候条件为例,对在该地区建设的大型地面光伏电站中光伏方阵容量分别选择3.125 MW和6.25 MW时的经济性及可行性进行了分析。结果显示:光伏方阵容量为6.25 MW时,其单瓦造价与光伏方阵容量为3.125 MW时的单瓦造价基本持平,因此在该地区选择6.25 MW光伏方阵容量的优势不明显。     

Analysis of off-grid hybrid wind turbine/solar PV water pumping systems

While many remote water pumping systems exist (e.g. mechanical windmills, solar photovoltaic, wind-electric, diesel powered), few combine both the wind and solar energy resources to possibly improve the reliability and the performance of the system. In this paper, off-grid wind turbine (WT) and solar photovoltaic (PV) array water pumping systems were analyzed individually and combined as a hybrid system. The objectives were to determine: (1) advantages or disadvantages of using a hybrid system over using a WT or a solar PV array alone; (2) if the WT or solar PV array interfered with the output of the other; and (3) which hybrid system was the most efficient for the location. The WT used in the analysis was rated at 900 W alternating current (AC). There were three different solar PV arrays analyzed, and they were rated at 320, 480, and 640 W direct current (DC). A rectifier converted the 3-phase variable voltage AC output from the WT to DC before combining it with the solar PV array DC output. The combined renewable energies powered a single helical pump. The independent variable used in the hybrid WT/PV array analysis was in units of W/m². The peak pump efficiency of the hybrid systems at Bushland, TX occurred for the 900 W WT combined with the 640 W PV array. The peak pump efficiencies at a 75 m pumping depth of the hybrid systems were: 47% (WT/320 W PV array), 51% (WT/480 W PV array), and 55% (WT/640 W PV array). Interference occurred between the WT and the different PV arrays (likely due to voltage mismatch between WT and PV array), but the least interference occurred for the WT/320 W PV array. This hybrid system pumped 28% more water during the greatest water demand month than the WT and PV systems would have pumped individually. An additional controller with a buck/boost converter is discussed at end of paper for improvement of the hybrid WT/PV array water pumping system.     

局部阴影条件下基于改进电导增量法的光伏系统最大功率跟踪方法

在局部阴影的情况下,由于串联式光伏组件的输出特性不同而产生多个极值点,使得传统的最大功率追踪（maximum power point tracking, MPPT）方法陷入局部极值点而失效。文中提出一种针对两级并网光伏系统的改进电导增量法以适应光伏阵列在局部阴影下的多峰值最大功率跟踪,通过分析最大功率点电压的变化范围,设定最大功率电压搜索范围以提高搜索效率,并通过DC/DC Boost变换器占空比实现输入电压控制,保证算法不陷入局部极值点。最后利用仿真实验验证了该算法在有、无阴影情况下均能准确地跟踪光伏方阵最大功率,有效提高了光伏阵列输出效率。     

An investigation on partial shading of PV modules with different connection configurations of PV cells

Partial shading is a commonly encountered issue in a PV (photovoltaic) system. In this paper, five different connection configurations of PV cells are studied to compare their performance under the condition of partial shading. They are SS (simple series), SP (series-parallel), TCT (total-cross-tied), BL (bridge-linked) and HC (honey comb) configurations. The electric network of each connection configuration is analyzed, taking into account the nonlinear nature of PV cells, by writing the Kirchhoff’s voltage and current equations. The analysis is followed by solving the simultaneous nonlinear equations using the Newton-Raphson algorithm, which allows the I-V (current-voltage) characteristic of the module with a specific configuration in response to different types and levels of partial shading to be evaluated. Comparison of the maximum power and fill factors of the five connection configurations is then carried out. Also studied is the reverse voltage across each PV cell. It is found that in most cases, the TCT configuration has a superior performance over the other four configurations in most comparison indices.