Performance analysis of the tracking of the global extreme on multimodal patterns using the Asymptotic Perturbed Extremum Seeking Control scheme

This paper presents the capability of the Asymptotic Perturbed Extremum Seeking Control (aPESC) scheme to track the Global Extreme on multimodal patterns. The multimodal patterns are simulated based on power characteristics generated by a photovoltaic (PV) array under Partial Shading Conditions (PSCs). The aPESC scheme is tested to evaluate the performance of locating, searching and tracking of the Global Maximum Power Point (GMPP). The following performance indicators such as the searching resolution, tracking accuracy, tracking efficiency, and tracking speed are used to compare the performance of the GMPP tracking (GMPPT) algorithms. The aPESCH1 scheme proposed has been implemented in MATLAB/Simulink package to evaluate the performance indicators mentioned above. The results prove that the proposed aPESCH1 scheme is effective and simple to be implemented.     

Designing and modelling of the asymptotic perturbed extremum seeking control scheme for tracking the global extreme

This paper presents the designing and modeling of the Asymptotic Perturbed Extremum Seeking Control (aPESC) scheme that is capable to locate and track the Global Extremes on the multimodal patterns. The multimodal patterns may appear on power generated by a photovoltaic (PV) array under Partial Shading Conditions (PSCs), but also on net power generated by a Fuel Cell (FC) system. The proposed aPESC scheme uses a scanning technique to determine the GMPP on different multimodal patterns based on two components of the searching signal: (1) the scanning signal locates the LMPP by sweeping the PV pattern based on a asymptotic dither modulated by the first harmonic of the PV power and controlled by the dither gain (k₂); (2) the tracking signal finds and tracks accurately the GMPP based on similar loop used in PESC schemes proposed in the literature that is controlled by the loop gain (k₁). These tuning parameters are designed based on the averaged model of this aPESC scheme. Also, the averaged scheme and local averaged loop of the aPESCH1 scheme are used to estimate the searching gradient and analyze the closed ESC loop stability. The design methodology is tested on generic multimodal patterns and then is validated considering a PV system and a FC system.     

一种改进型的太阳能最大功率点跟踪控制与仿真

从实际应用角度出发,论述了采用改进间歇扫描跟踪的方法进行最大功率点跟踪控制的过程,并通过仿真实验验证其可行性和有效性,从而达到了较好利用太阳能的目的。     

Analysis of MPPT characteristics in photovoltaic power system

This paper describes characteristics evaluation of the power conditioner which has the function of Maximum Power Point Tracking (MPPT) by “mountain climbing method” through computer simulations. The generated power on the constant voltage control is compared to the one on MPPT with the load matching correction factor (Kpm). In this simulation, the following parameters are chosen, the rate of the voltage ΔV on changing the operating point and of the voltage ΔV_c on checking the maximum point.As a result, the influence of these parameters on Kpm is showed and it is made clear that we should decide the MPPT parameters with care.     

A fast and low cost analog maximum power point tracking method for low power photovoltaic systems

Low power photovoltaic (PV) systems are commonly used in stand-alone applications. For these systems, a simple and cost-effective maximum power point tracking (MPPT) solution is essential. In this paper, a fast and low cost analog MPPT method for low power PV systems is proposed. By using two voltage approximation lines (VALs) to approximate the maximum power point (MPP) locus, a low-complexity analog MPPT circuit can be developed. Theoretical derivation and detailed design procedure will be provided in this paper. The proposed method boasts the advantages such as simple structure, low cost, fast tracking speed and high tracking efficiency. To validate the correctness of the proposed method, simulation and experimental results of an 87 W PV system will also be provided to demonstrate the effectiveness of the proposed technique.     

Design of a robust and efficient power electronic interface for the grid integration of solar photovoltaic generation systems

Nowadays, the penetration of photovoltaic (PV) solar power generation in distributed generation (DG) systems is growing rapidly. This condition imposes new requirements to the operation and management of the distribution grid, especially when high integration levels are achieved. Under this scenario, the power electronics technology plays a vital role in ensuring an effective grid integration of the PV system, since it is subject to requirements related not only to the variable source itself but also to its effects on the stability and operation of the electric grid. This paper proposes an enhanced interface for the grid connection of solar PV generation systems. The topology employed consists of a three-level cascaded Z-source inverter that allows the flexible, efficient and reliable generation of high quality electric power from the PV plant. A full detailed model is described and its control scheme is designed. The dynamic performance of the designed architecture is verified by computer simulations.     

Modeling and maximum power point tracking (MPPT) method for PV array under partial shade conditions

Influenced by partial shade, PV module aging or fault, there are multiple peaks on PV array's output power–voltage (P–V) characteristic curve. Conventional maximum power point tracking (MPPT) methods are effective for single peak P–V characteristic under uniform solar irradiation, but they may fail in global MPP tracking under multi-peak P–V characteristics. Existing methods in literature for this problem are still unsatisfactory in terms of effectiveness, complexity and speed. In this paper, we first analyze the mathematical model of PV array that is suitable for simulation of complex partial shade situation. Then an adaptive MPPT (AMPPT) method is proposed, which can find real global maximum power point (MPP) for different partial shade conditions. When output characteristic of PV array varies, AMPPT will adjust tracking strategies to search for global peak area (GPA). Then it is easy for conventional MPPT to track the global MPP in GPA. Simulation and experimental results verify that the proposed AMPPT method is able to find real global MPP accurately, quickly and smoothly for complex multi-peak P–V characteristics. Comparison analysis results demonstrate that AMPPT is more effective for most shade types.     

电路非理想参数对光伏系统最大功率追踪的影响

以光伏电池和Boost变换器构成的光伏系统为例,考虑实际电路元件的非理想参数,建立了含Boost变换器光伏系统的精确数学模型,研究了非理想参数对光伏系统最大功率追踪（MPPT）的影响, 并通过Simulink仿真及dSPACE试验验证。结果表明,当电路中存在非理想参数时,MPPT追踪的占空比和直流母线电压均会受到影响,也有可能会对原电路产生严重影响,甚至导致电路无法正常工作,因此在进行电路设计时一定要考虑电路非理想参数的影响,由此验证了理论分析的正确性。     

Maximum photovoltaic power tracking for the PV array using the fractional-order incremental conductance method

This paper proposes maximum photovoltaic power tracking (MPPT) for the photovoltaic (PV) array using the fractional-order incremental conductance method (FOICM). Since the PV array has low conversion efficiency, and the output power of PV array depends on the operation environments, such as various solar radiation, environment temperature, and weather conditions. Maximum charging power can be increased to a battery using a MPPT algorithm. The energy conversion of the absorbed solar light and cell temperature is directly transferred to the semiconductor, but electricity conduction has anomalous diffusion phenomena in inhomogeneous material. FOICM can provide a dynamic mathematical model to describe non-linear characteristics. The fractional-order incremental change as dynamic variable is used to adjust the PV array voltage toward the maximum power point. For a small-scale PV conversion system, the proposed method is validated by simulation with different operation environments. Compared with traditional methods, experimental results demonstrate the short tracking time and the practicality in MPPT of PV array.     

Analysis and enhancement of PV efficiency with incremental conductance MPPT technique under non-linear loading conditions

This paper presents experimental evaluations for variation in the efficiency of energy extracted from a photovoltaic (PV) module (under non-linear loading) incorporated with an incremental conductance(IC) maximum power point tracking (MPPT) algorithm. The focus is on the evaluation of the PV panel under non-linear loading conditions using the experimental installation of a 100W_p photovoltaic array connected to a DC–DC converter and a KVA inverter feeding a non-linear load. Under the conditions of non-linear loading, both the simulation and experiment show that the MPPT technique fails to attain maximum power point due to the presence of ripples in the current leading eventually to a reduction in efficiency. In this paper, panel current is taken as a function of load impedance in the MPPT algorithm to eradicate power variation, as load impedance varies with supply voltage under non-linear conditions. The system is simulated for different non-linear loads using MATLAB-Simulink. A TMDSSOLAREXPKIT was used for MPPT control. In case 2, the inverter is connected to a single phase grid. When a voltage swell occurs in the grid, PV power drops. This power loss is reduced using the proposed MPPT method. The results of simulations and experimental measurements and cost efficiency calculations are presented.     

基于步长优化的扰动观察法最大功率点跟踪算法研究

光伏阵列的功率输出极易受到光照强度、温度变化等环境因素的影响。为了保证光伏发电系统保持高效的输出,最大功率点跟踪技术就显得尤为重要。针对目前的最大功率点跟踪技术仍存在功率振荡、步长选择以及跟踪时间等问题,提出一种基于功率对电压的导数变化的变步长最大功率点跟踪算法。通过实时数字仿真器建立半实物125 kW“T”型三电平三相光伏发电系统,对比分析了改进型算法和传统两段步长算法的静态特性和动态特性,实验结果表明：所提出算法具有更好的有效性和实用性。     

A novel maximum power point tracking technique based on fuzzy logic for photovoltaic systems

Maximum power point tracking (MPPT) techniques are considered a crucial part in photovoltaic system design to maximise the output power of a photovoltaic array. Whilst several techniques have been designed, Perturb and Observe (P&O) is widely used for MPPT due to its low cost and simple implementation. Fuzzy logic (FL) is another common technique that achieves vastly improved performance for MPPT technique in terms of response speed and low fluctuation about the maximum power point. However, major issues of the conventional FL-MPPT are a drift problem associated with changing irradiance and complex implementation when compared with the P&O-MPPT. In this paper, a novel MPPT technique based on FL control and P&O algorithm is presented. The proposed method incorporates the advantages of the P&O-MPPT to account for slow and fast changes in solar irradiance and the reduced processing time for the FL-MPPT to address complex engineering problems when the membership functions are few. To evaluate the performance, the P&O-MPPT, FL-MPPT and the proposed method are simulated by a MATLAB-SIMULINK model for a grid-connected PV system. The EN 50530 standard test is used to calculate the efficiency of the proposed method under varying weather conditions. The simulation results demonstrate that the proposed technique accurately tracks the maximum power point and avoids the drift problem, whilst achieving efficiencies of greater than 99.6%.     

Fuzzy-PSO controller design for maximum power point tracking in photovoltaic system

Photovoltaic power generation system becomes increasingly important, highly attractive as a clean and renewable energy sources, widely used today in many applications. Recently, researchers have strongly promoted the use of solar energy as a viable source of energy due to its advantages and which it can be integrated into local and regional power supplies. The P–V curve of photovoltaic system exhibits multiple peaks under various conditions of functioning and changes in meteorological conditions which reduces the effectiveness of conventional maximum power point tracking (MPPT) methods and the Particle swarm optimization (PSO) algorithm is considered to be highly efficient for the solution of complicated problems.In this paper, the application of this approach based MPPT algorithm for Photovoltaic power generation system operating under variable conditions is proposed to optimize and to design an intelligent controller comparing to conventional one. PSO Approaches is considered to select and generate an optimal duty cycle which varies with photovoltaic parameters in order to extract the maximum Power. Simulation results show that the proposed approach can track the maximum power point faster and can improve the performance of the system compared to the conventional method.     

Comparative study and performance evaluation of central and distributed topologies of photovoltaic system

In this paper, we present a new alternative for improving both the performance of photovoltaic (PV) systems and the efficiency of the energy conversion by using different configuration of power converters. For this purpose, a comparative study between two configurations is carried out. The first configuration consists of a classical PV generator with a single centralized high power converter and the second one concerns a distributed topology. For this latter we use a certain number of PV strings with low power converters attached in series, in parallel or in a combination of series and parallel. Obviously the string topology has some advantages. Each power converter can control the power conversion of each module individually, which results in increased overall energy conversion of the entire system. The MPPT control system in this case can react effectively to atmospheric variations, to shading effect and to changes in the load. The PV system still operates even in case of failure on one of the power converters in a string. We simulated and compared the different conversion configurations in order to find the best one in terms of efficiency and produced energy. The obtained results are very interesting and can lead to optimal sizing and selection of best PV topology for a given application.     

An accurate method for the PV model identification based on a genetic algorithm and the interior-point method

Due to the PV module simulation requirements as well as recent applications of model-based controllers, the accurate photovoltaic (PV) model identification method is becoming essential to reduce the PV power losses effectively. The classical PV model identification methods use the manufacturers provided maximum power point (MPP) at the standard test condition (STC). However, the nominal operating cell temperature (NOCT) is the more practical condition and it is shown that the extracted model is not well suited to it. The proposed method in this paper estimates an accurate equivalent electrical circuit for the PV modules using both the STC and NOCT information provided by manufacturers. A multi-objective global optimization problem is formulated using only the main equation of the PV module at these two conditions that restrains the errors due to employing the experimental temperature coefficients. A novel combination of a genetic algorithm (GA) and the interior-point method (IPM) allows the proposed method to be fast and accurate regardless the PV technology. It is shown that the overall error, which is defined by the sum of the MPP errors of both the STC and the NOCT conditions, is improved by a factor between 5.1% and 31% depending on the PV technology.     

Quantitative field performance analysis of a photovoltaic array

A quantitative analysis of the long-term field performance of a photovoltaic (PV) array has been made considering such field variables as solar insolation, temperature and long-term degradation of a solar cell. It deals with (i) the numerical analysis of two degradation factors of a single crystal solar cell, namely, increased lumped series resistance R_s and decreased short circuit current I_sc, (ii) the field condition V_m — I_m relation, and (iii) the ratio of I_m and I_sc for a PV array. The value of I_m has been computed from the solution of a transcendental equation using Newton–Raphson approximation technique. This approach has been verified by field data obtained in Delhi, India, over a period of four years for the single crystal silicon PV modules (manufactured by CEL, India). It can be used for the study of the long-term field performance of a polycrystalline and amorphous silicon PV module.     

一种基于变换器拓扑的新型MPPT控制算法的研究

提出一种基于变换器拓扑（Boost／Buck）的最大功率点跟踪控制方法,该方法既能准确、稳定地跟踪到最大功率点,又只需对光伏输出电压这一个模拟量进行采样。同时,对所提出的该种方法进行了仿真建模分析,并比较了这几种MPPT算法下的跟踪效果。结果表明该方法具有更好的快速性、稳定性和经济性。     

Design of innovative power conditioning system for the grid integration of thermoelectric generators

Recently, thermoelectric generators (TEGs) have emerged as a potential alternative for clean energy generation, due mainly to the technology innovation and the marked cost reduction of modules, as well as their distinctive advantages. In a TEG system, the electronic power conditioning system (PCS) plays a vital role in ensuring the effective power grid integration, since it is subject to requirements related not only to the variable thermal source itself but also to its effects on the grid operation. This paper proposes an enhanced structure of PCS for the grid integration of TEG arrays to maximize the energy capture from a variable heat source. The innovative topology employed consists of a Z-source inverter that allows the flexible, efficient and reliable generation of high quality electric power from the TEG array. A full detailed model is described and its control scheme is designed. The dynamic performance of the proposed systems is fully validated by computer simulation and experimental studies.     

High-efficiency grid-connected photovoltaic module integrated converter system with high-speed communication interfaces for small-scale distribution power generation

This paper presents a high-efficiency grid-connected photovoltaic (PV) module integrated converter (MIC) system with reduced PV current variation. The proposed PV MIC system consists of a high-efficiency step-up DC-DC converter and a single-phase full-bridge DC-AC inverter. An active-clamping flyback converter with a voltage-doubler rectifier is proposed for the step-up DC-DC converter. The proposed step-up DC-DC converter reduces the switching losses by eliminating the reverse-recovery current of the output rectifying diodes. To reduce the PV current variation introduced by the grid-connected inverter, a PV current variation reduction method is also suggested. The suggested PV current variation reduction method reduces the PV current variation without any additional components. Moreover, for centralized power control of distributed PV MIC systems, a PV power control scheme with both a central control level and a local control level is presented. The central PV power control level controls the whole power production by sending out reference power signals to each individual PV MIC system. The proposed step-up DC-DC converter achieves a high-efficiency of 97.5% at 260 W output power to generate the DC-link voltage of 350 V from the PV voltage of 36.1 V. The PV MIC system including the DC-DC converter and the DC-AC inverter achieves a high-efficiency of 95% with the PV current ripple less than 3% variation of the rated PV current.     

Development of hybrid photovoltaic-fuel cell system for stand-alone application

In this paper we present firstly the different hybrid systems with fuel cell. Then, the study is given with a hybrid fuel cell–photovoltaic generator. The role of this system is the production of electricity without interruption in remote areas. It consists generally of a photovoltaic generator (PV), an alkaline water electrolyzer, a storage gas tank, a proton exchange membrane fuel cell (PEMFC), and power conditioning units (PCU) to manage the system operation of the hybrid system. Different topologies are competing for an optimal design of the hybrid photovoltaic–electrolyzer–fuel cell system. The studied system is proposed. PV subsystem work as a primary source, converting solar irradiation into electricity that is given to a DC bus. The second working subsystem is the electrolyzer which produces hydrogen and oxygen from water as a result of an electrochemical process. When there is an excess of solar generation available, the electrolyzer is turned on to begin producing hydrogen which is sent to a storage tank. The produced hydrogen is used by the third working subsystem (the fuel cell stack) which produces electrical energy to supply the DC bus. The modelisation of the global system is given and the obtained results are presented and discussed.