Six‐element circuit for maximum power point tracking in photovoltaic‐motor systems with variable‐frequency drives

A low‐cost circuit was developed for stable and efficient maximum power point (MPP) tracking in autonomous photovoltaic‐motor systems with variable‐frequency drives (VFDs). The circuit is made of two resistors, two capacitors, and two Zener diodes. Its input is the photovoltaic (PV) array voltage and its output feeds the proportional‐integral‐derivative (PID) controller usually integrated into the drive. The steady‐state frequency–voltage oscillations induced by the circuit were treated in a simplified mathematical model, which was validated by widely characterizing a PV‐powered centrifugal pump. General procedures for circuit and controller tuning were recommended based on model equations. The tracking circuit presented here is widely applicable to PV‐motor system with VFDs, offering an efficient open‐access technology of unique simplicity. Copyright © 2010 John Wiley & Sons, Ltd.     

基于DSP的光伏最大功率跟踪技术的研究

光伏电池的最大功率点受光照强度、环境温度和负载大小等外界因素的影响而不断变化,因此很有必要对光伏电池的最大功率点进行时时跟踪以提高光伏电池的利用率.以分析光伏电池输出特性为基础,在实验室环境下用直流电源和可变电阻来模拟光伏电池,并选择Boost电路实现DC/DC变换来搭建实验电路;同时该实验采用DSP(TMS320F2812)作为控制器来进行最大功率跟踪算法的控制.实验结果表明,该方法可以有效地完成光伏的最大功率跟踪.     

Comparative study of maximum power point tracking algorithms

Maximum power point trackers (MPPTs) play an important role in photovoltaic (PV) power systems because they maximize the power output from a PV system for a given set of conditions, and therefore maximize the array efficiency. Thus, an MPPT can minimize the overall system cost. MPPTs find and maintain operation at the maximum power point, using an MPPT algorithm. Many such algorithms have been proposed. However, one particular algorithm, the perturb‐and‐observe (P&O) method, claimed by many in the literature to be inferior to others, continues to be by far the most widely used method in commercial PV MPPTs. Part of the reason for this is that the published comparisons between methods do not include an experimental comparison between multiple algorithms with all algorithms optimized and a standardized MPPT hardware. This paper provides such a comparison. MPPT algorithm performance is quantified through the MPPT efficiency. In this work, results are obtained for three optimized algorithms, using a microprocessor‐controlled MPPT operating from a PV array and also a PV array simulator. It is found that the P&O method, when properly optimized, can have MPPT efficiencies well in excess of 97%, and is highly competitive against other MPPT algorithms. Copyright © 2002 John Wiley & Sons, Ltd.     

A refrigeration facility for milk cooling powered by photovoltaic solar energy

The use of renewable energy sources is usually a reliable alternative in rural areas and developing countries, where the grid line does not exist or is at a great distance. In this work, the characteristics and working conditions of a refrigeration facility designed for cooling down an expected daily production of 150 l of milk are analyzed. The facility is a stand‐alone, direct‐coupled system where 20 photovoltaic modules, 120 W_p each, power two permanent magnet, direct current motors of 24 V, 650 W. Each motor drives a separate cooling system compressor, which provides the flexibility to operate the equipment with one or two motors and with various interconnections of the PV modules, depending on the available irradiance level and the thermodynamic state of the system. The photovoltaic energy obtained during daylight hours is stored in the form of sensible and latent heat of frozen water in a tank surrounding a milk container. Thermodynamic analysis of the system shows that the autonomy of the system is 2·5 consecutive cloudy days if the available stored ice energy is 80% of the nominal capacity of the water/ice tank. Results of the refrigeration efficiency are similar to those obtained by other commercial refrigeration facilities powered by a photovoltaic array, including batteries. Copyright © 2003 John Wiley & Sons, Ltd.     

Comparative study of maximum power point tracking techniques for hybrid renewable energy system

The power generation demand is increasing day-by-day throughout the world, therefore, the use of hybrid systems becomes a significant solution. The hybrid renewable energy system (HRES) is used for delivering power in various regions in order to overcome intermittence of wind and solar resources. Because of increasing environmental problems, for example, greenhouse gas emission and energy cost have interested novel research into substitute methods in favour of electrical power generation. Maximum Power Point Tracking (MPPT) control method is a vast deal of novel research used for enhancing the efficiency of HRES. The authors have revealed that the hybrid techniques i.e. Global MPPT, fuzzy-neuro systems, Adaptive Neuro-Fuzzy Inference System (ANFIS), Perturbed and Observe (P&O) + Adaptive Neural Network (ANN) etc. can provide best results as compared to other MPPT control methods. This paper offering a state of art review of MPPT control techniques for HRES.     

Characterisation of charge voltage of lead‐acid batteries: application to the charge control strategy in photovoltaic systems

In stand‐alone photovoltaic (PV) systems, charge controllers prevent excessive battery overcharge by interrupting or limiting the current flow from the PV array to the battery when the battery becomes fully charged. Charge regulation is most often accomplished by limiting the battery voltage to a predetermined value or cut‐off voltage, higher than the gassing voltage. These regulation voltages are dependent on the temperature and battery charge current. An adequate selection of overcharge cut‐off voltage for each battery type and operating conditions would maintain the highest battery state of charge without causing significant overcharge thus improving battery performance and reliability. To perform this work, a sample of nine different lead‐acid batteries, typically used in stand‐alone PV systems including vented and sealed batteries with 2 V cells and monoblock configurations have been selected. This paper presents simple mathematical expressions fitting two charge characteristic voltages: the gassing voltage (V_g) and the end‐of charge voltage (V_fc) as function of charge current and temperature for the tested batteries. With these expressions, we have calculated V_g and V_fc at different current rates. An analysis of the different values obtained is presented here focusing in the implication in control strategies of batteries in stand‐alone PV systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Dynamic performance of maximum power point tracking circuits using sinusoidal extremum seeking control for photovoltaic generation

The article studies the dynamic performance of a family of maximum power point tracking circuits used for photovoltaic generation. It revisits the sinusoidal extremum seeking control (ESC) technique which can be considered as a particular subgroup of the Perturb and Observe algorithms. The sinusoidal ESC technique consists of adding a small sinusoidal disturbance to the input and processing the perturbed output to drive the operating point at its maximum. The output processing involves a synchronous multiplication and a filtering stage. The filter instance determines the dynamic performance of the MPPT based on sinusoidal ESC principle. The approach uses the well-known root-locus method to give insight about damping degree and settlement time of maximum-seeking waveforms. This article shows the transient waveforms in three different filter instances to illustrate the approach. Finally, an experimental prototype corroborates the dynamic analysis.     

Comparative analysis of maximum power point tracking controller for wind energy system

This paper proposes an adaptive maximum power point tracking (MPPT) control method to achieve the maximum power from the wind turbine (WT) power generation system. The MPPT control method has a vital role to find the maximum power point, and also compute the simulation results in both analysis such as offline using MATLAB/SIMULINK? and online using OPAL-RT simulator. The proposed adaptive perturb and observe (P&;O) algorithm provides better results using the OPAL-RT simulator compared to the P&;O method using MATLAB/SIMULINK?. The power generation through doubly fed induction generator (DFIG) WT system is becoming important day by day throughout the world. The simulation result by OPAL-RT simulator showed that the efficiency of WT-DFIG has been enhanced.     

光伏系统最大功率跟踪技术的研究

基于传统的滑膜控制算法,本文采用一种改进的指数趋近律方法,来实现最大功率跟踪,使得控制输出变量可以为连续变量,再通过调制器得到开关管的控制信号,实现控制,以弥补传统方法的参数灵敏度、适用范围受限制等方面的缺陷。通过对传统算法和改进算法的仿真比较,得出了改进的滑模控制法能够快速地跟踪最大功率点,振荡幅度较小,鲁棒性较好。     

A model for the simulation of energy gains when using distributed maximum power point tracking (DMPPT) in photovoltaic arrays

Over the past years, the photovoltaic (PV) market has been invaded with numerous power optimizers and micro‐inverters that claim large energy gains when used in PV generators with shading or module mismatch. These products provide distributed maximum power point tracking (DMPPT), normally at module level, allowing the maximum power to be extracted from each PV module. This topology can be beneficial in situations where the PV generator is shaded or when there is large module mismatch. However, it is not clear that this power gain will result in energy improvements over a whole year or the lifetime of the system. This paper presents a very detailed and precise model for simulating energy gains with DMPPT as well as its verification and simulation results with different shading profiles, showing the possible energy gain over a whole year. Simulation results show that the yearly energy gain is much lower than the maximum power gain. However, interesting yearly gains of up to 12% are obtained in one of the simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

风光互补发电系统最大功率跟踪综述

风光互补发电系统的运行需要快速准确地进行最大功率点跟踪,为此综述了风光互补发电系统最大功率点跟踪的几种方法,包括在太阳能电池阵列部分日益成熟、改进和优化策略较多的扰动观察法、电导增量法和恒压控制法;风力发电机部分的叶尖速比控制法、功率信号反馈法、扰动观察法,分别说明了各种跟踪控制方法的优点和不足之处。最后探讨了最大功率点跟踪控制方法的发展思路,对该领域今后的研究方向做了展望。     

Toward multiple maximum power point estimation of photovoltaic systems based on semiconductor theory

Environmental conditions, such as temperature, non‐uniform irradiation, and solar shading, deeply affect the characteristics of photovoltaic (PV) modules in PV‐assisted generation systems. Several local maximum power points (MPPs) are found in the power–voltage curve of PV systems constructed by series/parallel‐connected PV modules under partially shaded conditions. The characteristics of PV systems change unpredictably when multiple MPPs occur, so the actual MPP tracking (MPPT) becomes a difficult task. Conventional MPPT methods for the PV systems under partially shaded conditions cannot quickly find the actual MPP such that the optimal utilization of PV systems cannot be achieved. Based on the p–n junction semiconductor theory, we develop a multipoint direct‐estimation (MPDE) method to directly estimate the multiple MPPs of the PV systems under partially shaded conditions and to cope with the mentioned difficulties. Using the proposed MPDE method, the multiple MPPs of the PV systems under partially shaded conditions can be directly determined from their irradiated current–voltage and power–voltage characteristic curves. The performances of the proposed MPDE method are evaluated by examining the characteristics of multiple MPPs of PV systems with respect to different shading strengths and numbers of the shaded PV modules and also tested using the field data. The experimental results demonstrate that the proposed MPDE method can simply and accurately estimate the multiple MPPs of the PV systems under partially shaded conditions. The optimization of MPP control models and the MPPT for PV systems could be achieved promisingly by applying the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.     

Microcontroller‐based simple maximum power point tracking controller for single‐stage solar stand‐alone water pumping system

A simple microcontroller‐based maximum power point tracking controller is proposed for a single‐stage solar stand‐alone water pumping system for remote, isolated, and nonelectrified population, where less maintenance, low cost, and an efficient system is of prime interest. It consists of a photovoltaic (PV) module, a DC–AC converter utilizing space‐vector pulse‐width modulation, an induction motor coupled with a water pump, a voltage sensor, and a current sensor. A space‐vector pulse‐width modulation‐controlled DC–AC converter aided by a fast‐acting on–off supervisory controller with a modified perturb‐and‐observe algorithm performs both the functions of converting PV output voltage to a variable voltage, variable frequency output, as well as extracting the maximum power. A limited variable step size is preferred during transient state, and a steady frequency, which is calculated on the basis of steady‐state oscillation, is set during steady state. A fast‐acting on–off supervisory controller regulates DC link voltage during steady state and enables maximum power point tracking algorithm only during transient state to draw a new voltage reference. In the event of low voltage, the controller switches off the motor but continuously scans for an available PV voltage. The system is not protected against an overcurrent because the maximum current is equal to its short circuit current. The 16‐bit microcontroller dsPIC6010A (Microchip Technology, Inc., Chandler, AZ, USA) is used to implement the control functions. The proposed controller is verified through simulation as well as tested in the laboratory prototype model. The simulation and experimental results show good correlation. Copyright © 2011 John Wiley & Sons, Ltd.     

基于短路电流和扰动观察的光伏最大功率跟踪

在光伏最大功率跟踪（maximum power point tracking,MPPT）系统中,针对传统的扰动观察法（perturbation and observation,P＆O）难以同时满足跟踪速度和精度要求的问题,在原有的短路电流法的基础上,引入一种改进的扰动观察法,该算法不仅能够消除最大功率点附近的震荡,而且还能有效地提高响应速度.利用MATLAB/Simulink平台进行仿真,实验结果表明了算法的有效性.     

A novel analytical model for determining the maximum power point of thin film photovoltaic module

Achieving the maximum power output from photovoltaic (PV) modules is indispensable for the operation of grid‐connected PV power systems under varied atmospheric conditions. In recent years, the study of PV energy for different applications has attracted more and more attention because solar energy is clean and renewable. We propose an efficient direct‐prediction method to enhance the utilization efficiency of thin film PV modules by tackling the problem of tracking time and overcoming the difficulty of calculation. The proposed method is based on the p–n junction recombination mechanism and can be applied to all kinds of PV modules. Its performance is not influenced by weather conditions such as illumination or temperature. The experimental results show that the proposed method provides high‐accuracy estimation of the maximum power point (MPP) for thin film PV modules with an average error of 1.68% and 1.65% under various irradiation intensities and temperatures, respectively. The experimental results confirm that the proposed method can simply and accurately estimate the MPP for thin film PV modules under various irradiation intensities and temperatures. In future, the proposed method will be used to shed light on the optimization of the MPP tracking control model in PV systems. Copyright © 2012 John Wiley & Sons, Ltd.