Granular control of photovoltaic arrays by means of a multi‐output Maximum Power Point Tracking algorithm

In this paper, a Distributed Maximum Power Point Tracking (D‐MPPT) approach in photovoltaic (PV) applications is discussed. The proposed control method is suitable for the granular control of the PV generator at a module level or even at a sub‐module level. D‐MPPT is usually implemented by means of independent converters, each one of them running its own MPPT algorithm. Instead, the architecture proposed in this paper consists of only one digital controller, implementing a multivariable MPPT algorithm based on the Perturb and Observe approach, acting on a number of dc/dc converters, each one of them dedicated to a single PV module. The proposed control strategy reduces the number of current sensors with respect to the classical D‐MPPT architecture and tracks the maximum power evaluated at the dc/dc converters' output. Planar solid immersion mirror simulations and experimental results confirm the validity of the approach and of the design guidelines proposed in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

基于双并联Boost电路的光伏系统最大功率点跟踪控制方法

光伏电池的输出功率取决于外界环境（温度和光照条件）和负载状况,需采用最大功率点跟踪（MPPT）电路,才能使光伏电池始终输出最大功率,从而充分发挥光伏器件的光电转换效能.在比较了常用光伏发电系统控制的优缺点后,依据MPPT控制算法的基本工作原理,主电路采用双并联Boost电路,具有电压提升功能,并且能够提高DC-DC环节的额定功率和减小直流母线电压的纹波.针对传统扰动观察法存在的振荡和误判问题,提出了一种新型的基于双并联Boost电路的改进扰动观察法最大功率跟踪策略.在Matlab/Simulink下进行了建模与仿真,仿真结果表明,当外界环境发生变化时,系统能快速准确跟踪此变化,避免算法误判现象的发生,通过改变当前的负载阻抗,使之与光伏电池的输出阻抗等值相匹配采满足最大功率输出的要求,使系统始终工作在最大功率点处,并且在最大功率点处具有很好的稳态性能.最后通过实验验证了该算法的有效性.     

Analysis and design of phase‐interleaving series‐connected module‐integrated converter for DC‐link ripple reduction of multi‐stage photovoltaic power systems

Recently, installation of photovoltaic power systems such as building‐integrated photovoltaic in urban area has been spotlighted in renewable energy engineering field, even at the expense of the performance degradation from partial shading. The efficiency degradation of maximum power point tracking (MPPT) performance can be compensated by a kind of power‐conditioning system architecture such as module‐integrated converters (MIC), which can handle the optimal‐operation tracking for its own photovoltaic (PV) module. In case of a MIC with series‐connected outputs, it is easy to obtain a high DC‐link voltage for multiple stage PV power conditioning applications. However, switching ripple of the DC‐link voltage also increases as number of the modules increases. In this paper, as a solution for the ripple reduction, interleaved pulse width modulation‐phase synchronizing method is applied to the PV MIC modules. The switching‐ripple analysis of the MPPT power modules were performed and compared between the cases such as phase control or not. For the implementation of the phase control among the modules, Zigbee (XBee Pro, Digi International, Minnetonka, MN, USA) wireless communications transceiver and DSP (TMS320F28335, Texas Instruments, Dallas, TX, USA) series communications interface are utilized. Hardware prototype of the double‐module boost‐type 80‐W MICs has been built to validate the DC‐link voltage ripple reduction. Copyright © 2012 John Wiley & Sons, Ltd.     

A PSO‐based maximum power point tracking for photovoltaic systems under environmental and partially shaded conditions

To increase the efficiency of photovoltaic (PV) systems, maximum power point (MPP) tracking of the solar arrays is needed. Solar arrays output power depends on the solar irradiance and temperature. Also the mismatch phenomenon caused by partial shade will affect the output power of solar systems and lead to the incorrect operation of conventional MPP tracker. Under partially shaded conditions, the solar array power–current characteristic has multiple maximum. This paper presents a maximum power point tracking (MPPT) with particle swarm optimization method for PV systems under partially shaded condition. The performance of the proposed method is compared with perturb and observe (P&O), improved P&O, voltage‐based maximum power point tracking and current‐based maximum power point tracking algorithms, especially, under partially shaded condition. Simulation results confirm that proposed MPPT algorithm with high accuracy can track the peak power point under different insolation, temperature and partially shaded conditions, and it has the best performance in comparison with four mentioned MPPT algorithms. Also under rapidly changing atmospheric conditions, the P&O algorithm is diverged. Copyright © 2013 John Wiley & Sons, Ltd.     

光伏电池输出特性与最大功率点跟踪的仿真分析

根据太阳能光伏电池的等效电路特点,建立了相应的光伏电池组件的仿真模型。该模型可以实现在不同光照强度和温度下光伏组件的输出特性,在此模型基础上研究了光伏组件最大功率追踪方法(MPPT)。在众多最大功率追踪方法中,扰动法有着比较优秀的控制效果。针对最常用的最大功率点跟踪方法-扰动观察法,提出一种改进型的扰动法算法,通过仿真结果和实验证明该方法在一定程度上可解决光伏电池输出非线性的问题,有效避免跟踪偏差,提高光伏电池的输出效率,且动态响应速度快,使光伏系统具有良好的动态和稳态性能。     

An enhanced scanning-based MPPT approach for DMPPT systems

In this paper, an improved maximum power point tracking (MPPT) approach being low parameter dependency, simple structure and limited search interval has been presented for distributed MPPT photovoltaic (PV) systems. Basically, this approach is based on scanning of power–voltage (P-V) characteristic curve of PV modules in a limited duty ratio interval which makes tracking operation simple, fast and efficiently available in both uniform irradiance and partial shading conditions (PSCs). By limiting the scanning interval of maximum and minimum values of duty ratio via some analyses related to P-V characteristic for PSCs, global MPPT (GMPPT) is achieved in an efficient way. So as to validate performance of the proposed approach, a single-ended primary inductance converter has been used in both simulation and experimental studies. PV simulator has been used as a PV source to obtain different module characteristics with different number of bypass diodes and PV power levels. Both simulation and experimental results clarify that improved MPPT approach realises GMPPT effectively. Due to the high performance results, this approach can be an alternative technique in module-integrated converters, smart modules and PV power optimisers in which single module is used.     

Analytical study and evaluation results of power optimizers for distributed power conditioning in photovoltaic arrays

The use of modular or ‘micro’ maximum power point tracking (MPPT) converters at module level in series association, commercially known as “power optimizers”, allows the individual adaptation of each panel to the load, solving part of the problems related to partial shadows and different tilt and/or orientation angles of the photovoltaic (PV) modules. This is particularly relevant in building integrated PV systems. This paper presents useful behavioural analytical studies of cascade MPPT converters and evaluation test results of a prototype developed under a Spanish national research project. On the one hand, this work focuses on the development of new useful expressions which can be used to identify the behaviour of individual MPPT converters applied to each module and connected in series, in a typical grid‐connected PV system. On the other hand, a novel characterization method of MPPT converters is developed, and experimental results of the prototype are obtained: when individual partial shading is applied, and they are connected in a typical grid connected PV array. Copyright © 2011 John Wiley & Sons, Ltd.     

Modeling and Control of PV Charger System With SEPIC Converter

The photovoltaic (PV) stand-alone system requires a battery charger for energy storage. This paper presents the modeling and controller design of the PV charger system implemented with the single-ended primary inductance converter (SEPIC). The designed SEPIC employs the peak-current-mode control with the current command generated from the input PV voltage regulating loop, where the voltage command is determined by both the PV module maximum power point tracking (MPPT) control loop and the battery charging loop. The control objective is to balance the power flow from the PV module to the battery and the load such that the PV power is utilized effectively and the battery is charged with three charging stages. This paper gives a detailed modeling of the SEPIC with the PV module input and peak-current-mode control first. Accordingly, the PV voltage controller, as well as the adaptive MPPT controller, is designed. An 80-W prototype system is built. The effectiveness of the proposed methods is proved with some simulation and experimental results.     

5kW光伏并网发电系统及其仿真研究

随着新能源发电的迅速发展,越来越多的可再生能源被转化为电能并通过并网逆变器输送到电网。利用MATLAB仿真工具箱建立了由光伏阵列输出、Boost升压电路、逆变器、控制器、电网等组成的5 kW光伏并网发电系统的仿真模型,研究了光伏并网系统的特性。采用变结构模糊PID控制器实现5 kW光伏发电系统的MPPT;采样电网电压作为逆变器电流的参考信号,利用滞环比较法控制逆变器,实现系统输出电流与电网电压同频同相,功率因素近似为1。仿真结果表明,系统较好地实现了光伏发电系统的MPPT及安全并网,对实际光伏并网系统的设计有参考意义。     

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.     

Performance evaluation of a MPPT controller with model predictive control for a photovoltaic system

ABSTRACT

Efficiency has been a major factor in the growth of photovoltaic (PV) systems. Different control techniques have been explored to extract maximum power from PV systems under varying environmental conditions. This paper evaluates the performance of a new improved control technique known as model predictive control (MPC) in power extraction from PV systems. Exploiting the ability of MPC to predict future state of controlled variables, MPC has been implemented for tacking of maximum power point (MPP) of a PV system. Application of MPC for maximum power point tracking (MPPT) has been found to result into faster tracking of MPP under continuously varying atmospheric conditions providing an efficient system. It helps in reducing unwanted oscillations with an increase in tracking speed. A detailed step by step process of designing a model predictive controller has been discussed. Here, MPC has been applied in conjunction with conventional perturb and observe (P&O) method for controlling the dc-dc boost converter switching, harvesting maximum power from a PV array. The results of MPC controller has been compared with two widely used conventional methods of MPPT, viz. incremental conductance method and P&O method. The MPC controller scheme has been designed, implemented and tested in MATLAB/Simulink environment and has also been experimentally validated using a laboratory prototype of a PV system.     

基于MATLAB光伏并网逆变系统的仿真研究

光伏并网发电系统是光伏发电系统发展的趋势。文中介绍了单极式光伏系统的拓扑结构和实现最大功率的工作原理,阐述了电导增量法实现MPPT的基本思想。根据光伏系统并网发电拓扑结构,设计了一套新型的实现最大功率跟踪的单极式光伏并网逆变器。逆变器控制部分由DSP实现最大功率跟踪和输出电流跟踪控制,实现了逆变输出电流与电网同步,且高功率因数运行。仿真结果表明,单极式光伏并网逆变系统能准确跟踪太阳能电池最大功率点,并具有较好的稳定性。     

A high-efficiency single-phase three-wire photovoltaic energy conversion system

A single-phase three-wire photovoltaic energy conversion system with single-stage structure using a novel maximum power-point tracking (MPPT) algorithm is presented. An equivalent model of the proposed system is derived to analyze the characteristics of the system and to design the controller. Owing to the linear relation of the PV array parameters versus insolation, the model is easy to analyze. The proposed system employs a three-leg inverter to control the MPPT process, the line current, and neutral line current. A current-controlled MPPT algorithm controls the MPPT. A neutral line-mode controller maintains a utility neutral line current of zero. A line-mode controller controls the line current so as to provide power to the utility with a unity power factor. The proposed system acts as a solar generator on sunny days and functions as an active power filter on rainy days. Computer simulation and experimental results demonstrate the accuracy and the superior performance of the proposed technique.     

Development of a microcontroller-based, photovoltaic maximum powerpoint tracking control system

Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m² and 25°C     

Integrated photovoltaic maximum power point tracking converter

A low-power low-cost highly efficient maximum power point tracker (MPPT) to be integrated into a photovoltaic (PV) panel is proposed. This can result in a 25% energy enhancement compared to a standard photovoltaic panel, while performing functions like battery voltage regulation and matching of the PV array with the load. Instead of using an externally connected MPPT, it is proposed to use an integrated MPPT converter as part of the PV panel. It is proposed that this integrated MPPT uses a simple controller in order to be cost effective. Furthermore, the power converter has to be very efficient, in order to transfer more energy to the load than a directly-coupled system. This is achieved by using a simple soft-switched topology. A much higher conversion efficiency at lower cost will then result, making the MPPT an affordable solution for small PV energy systems     

Grid-Connected Photovoltaic Multistring PCS With PV Current Variation Reduction Control

In this paper, a grid-connected photovoltaic (PV) multistring power conditioning system with PV input current reduction control is proposed. An improved maximum power point tracking (MPPT) method for the multistring converter is suggested. The suggested MPPT algorithm tracks the maximum power point even though measurement errors exist. To reduce the PV current variation introduced by the inverter, a PV current variation reduction control is suggested. This PV current variation reduction control reduces the PV current variation without additional components. The low current variation reduces the filter size and improves the MPPT efficiency. All algorithms and controllers are implemented on a single-chip microcontroller. Experimental results obtained on a 3-kW prototype show high performance such as a MPPT efficiency of 99.7%, an almost unity power factor, a power efficiency of 96.7%, and a total harmonic distortion of 2.0%.     

Residential photovoltaic energy storage system

This paper introduces a residential photovoltaic (PV) energy storage system, in which the PV power is controlled by a DC-DC power converter and transferred to a small battery energy storage system (BESS). For managing the power, a pattern of daily operation considering the load characteristic of the homeowner, the generation characteristic of the PV power, and the power-leveling demand of the electric utility is prescribed. The system looks up the pattern to select the operation mode, so that powers from the PV array, the batteries and the utility are utilized in a cost-effective manner. As for the control of the system, a novel control technique for the maximum power-point tracking (MPPT) of the PV array is proposed, in which the state-averaged model of the DC-DC power converter, including the dynamic model of the PV array, is derived. Accordingly, a high-performance discrete MPPT controller that tracks the maximum power point with zero-slope regulation and current-mode control is presented. With proposed arrangements on the control of the BESS and the current-to-power scaling factor setting, the DC-DC power converter is capable of combining with the BESS for performing the functions of power conditioning and active power filtering. An experimental 600 W system is implemented, and some simulation and experimental results are provided to demonstrate the effectiveness of the proposed system     

Enhanced power quality based single phase photovoltaic distributed generation system

This article presents a novel control strategy for a 1-? 2-level grid-tie photovoltaic (PV) inverter to enhance the power quality (PQ) of a PV distributed generation (PVDG) system. The objective is to obtain the maximum benefits from the grid-tie PV inverter by introducing current harmonics as well as reactive power compensation schemes in its control strategy, thereby controlling the PV inverter to achieve multiple functions in the PVDG system such as: (1) active power flow control between the PV inverter and the grid, (2) reactive power compensation, and (3) grid current harmonics compensation. A PQ enhancement controller (PQEC) has been designed to achieve the aforementioned objectives. The issue of underutilisation of the PV inverter in nighttime has also been addressed in this article and for the optimal use of the system; the PV inverter is used as a shunt active power filter in nighttime. A prototype model of the proposed system is developed in the laboratory, to validate the effectiveness of the control scheme, and is tested with the help of the dSPACE DS1104 platform.     

An analysis of reliability in the early stages of photovoltaic systems in Japan

In order to disseminate Photovoltaic (PV) technologies into the energy network, the cost down is not only important, but also improving the performance of the PV system is significant issues. Long‐term reliability is one of the most important issues in terms of PV system performance. Previous researches were mainly focused on the reliability of PV modules, but the PV system is composed of a power conditioner, wiring, junction box, and so on. To improve the reliability of PV systems, it is important to accumulate trouble cases focused on all components of PV system. In this paper, we aim at evaluation of the reliability for the PV system on the early stages of PV system's lifetime by using large number of Japanese PV systems' data from the field Test in Japan. New Energy and Industrial Technology Development Organization has been running the “Field test project in Japan” from 1992. In this project, PV system users have cooperated with the collection of monitoring data and reported on the information of maintenance and certain failures of PV systems for 4 years after installation of PV system. Using those reports each year of installation, we evaluated reliability of PV systems by means of parameters such as Mean Time Between Failure, Mean Time To Repair, and the suspension time of PV system. As a result, the main trouble of PV systems was related power conditioner, and a few trouble of PV module was caused by typhoon. Moreover, the trend of the failure rate before FY 2000 of installation was demonstrated as the trend of initial failure in “bathtub curve;” however, the trend of its after FY 2001 of installation was indicated as the accidental failure in “bathtub curve.” Further, the operator simply forgot to restart the power conditioner after maintenance or suspensions of PV system in many trouble cases, and the user did not notice that it had been suspended for a while. These trouble cases can be avoidable easily through the effective alarm such as error message of power conditioner systems with monitoring systems. Thereby, monitoring with the evaluation method of PV systems is one of the important technologies due to the long‐term reliability and stable operation. Copyright © 2010 John Wiley & Sons, Ltd.