Showing papers on "Maximum power point tracking published in 2008"

A Variable Step Size INC MPPT Method for PV Systems

Abstract: Maximum power point tracking (MPPT) techniques are employed in photovoltaic (PV) systems to make full utilization of PV array output power which depends on solar irradiation and ambient temperature. Among all the MPPT strategies, the incremental conductance (INC) algorithm is widely used due to the high tracking accuracy at steady state and good adaptability to the rapidly changing atmospheric conditions. In this paper, a modified variable step size INC MPPT algorithm is proposed, which automatically adjusts the step size to track the PV array maximum power point. Compared with the conventional fixed step size method, the proposed approach can effectively improve the MPPT speed and accuracy simultaneously. Furthermore, it is simple and can be easily implemented in digital signal processors. A theoretical analysis and the design principle of the proposed method are provided and its feasibility is also verified by simulation and experimental results.

MATLAB-Based Modeling to Study the Effects of Partial Shading on PV Array Characteristics

Abstract: The performance of a photovoltaic (PV) array is affected by temperature, solar insolation, shading, and array configuration. Often, the PV arrays get shadowed, completely or partially, by the passing clouds, neighboring buildings and towers, trees, and utility and telephone poles. The situation is of particular interest in case of large PV installations such as those used in distributed power generation schemes. Under partially shaded conditions, the PV characteristics get more complex with multiple peaks. Yet, it is very important to understand and predict them in order to extract the maximum possible power. This paper presents a MATLAB-based modeling and simulation scheme suitable for studying the I-V and P-V characteristics of a PV array under a nonuniform insolation due to partial shading. It can also be used for developing and evaluating new maximum power point tracking techniques, especially for partially shaded conditions. The proposed models conveniently interface with the models of power electronic converters, which is a very useful feature. It can also be used as a tool to study the effects of shading patterns on PV panels having different configurations. It is observed that, for a given number of PV modules, the array configuration (how many modules in series and how many in parallel) significantly affects the maximum available power under partially shaded conditions. This is another aspect to which the developed tool can be applied. The model has been experimentally validated and the usefulness of this research is highlighted with the help of several illustrations. The MATLAB code of the developed model is freely available for download.

Maximum Power Point Tracking Scheme for PV Systems Operating Under Partially Shaded Conditions

Abstract: Current-voltage and power-voltage characteristics of large photovoltaic (PV) arrays under partially shaded conditions are characterized by multiple steps and peaks. This makes the tracking of the actual maximum power point (MPP) [global peak (GP)] a difficult task. In addition, most of the existing schemes are unable to extract maximum power from the PV array under these conditions. This paper proposes a novel algorithm to track the global power peak under partially shaded conditions. The formulation of the algorithm is based on several critical observations made out of an extensive study of the PV characteristics and the behavior of the global and local peaks under partially shaded conditions. The proposed algorithm works in conjunction with a DC-DC converter to track the GP. In order to accelerate the tracking speed, a feedforward control scheme for operating the DC-DC converter is also proposed, which uses the reference voltage information from the tracking algorithm to shift the operation toward the MPP. The tracking time with this controller is about one-tenth as compared to a conventional controller. All the observations and conclusions, including simulation and experimental results, are presented.

Power Management of a Stand-Alone Wind/Photovoltaic/Fuel Cell Energy System

Abstract: This paper proposes an AC-linked hybrid wind/photovoltaic (PV)/fuel cell (FC) alternative energy system for stand-alone applications. Wind and PV are the primary power sources of the system, and an FC-electrolyzer combination is used as a backup and a long-term storage system. An overall power management strategy is designed for the proposed system to manage power flows among the different energy sources and the storage unit in the system. A simulation model for the hybrid energy system has been developed using MATLAB/Simulink. The system performance under different scenarios has been verified by carrying out simulation studies using a practical load demand profile and real weather data.

Power supply system of vehicle

Abstract: PROBLEM TO BE SOLVED: To provide a power supply system of a vehicle, which can reduce a decline in power performance of a vehicle when it uses a plurality of power supplies in a switching manner or can prevent an excessive current flow when switching the power supplies. SOLUTION: A power supply system of a vehicle is equipped with inverters 14 and 22 which are supplied with electric power from batteries BA, BB1 and BB2; a connecting section 39B for connecting either one of the batteries BB1 and BB2 selectively to the inverters 14 and 22 so as to supply electric power to them; an air conditioner 40 which is supplied with electric power from the battery BA. When the battery (BB1 or BB2) to be selected is changed, a controller 30 stops the operation of the air conditioner 40 temporarily until the change in the connecting section 39B is completed. COPYRIGHT: (C)2010,JPO&INPIT

Reliability Issues in Photovoltaic Power Processing Systems

Abstract: Power processing systems will be a key factor of future photovoltaic (PV) applications. They will play a central role in transferring, to the load and/or to the grid, the electric power produced by the high-efficiency PV cells of the next generation. In order to come up the expectations related to the use of solar energy for producing electrical energy, such systems must ensure high efficiency, modularity, and, particularly, high reliability. The goal of this paper is to provide an overview of the open problems related to PV power processing systems and to focus the attention of researchers and industries on present and future challenges in this field.

Distributed Maximum Power Point Tracking of Photovoltaic Arrays: Novel Approach and System Analysis

Abstract: One of the major drawbacks of photovoltaic (PV) systems is represented by the effect of module mismatching and of partial shading of the PV field. Distributed maximum power point tracking (DMPPT) is a very promising technique that allows the increase of efficiency and reliability of such systems. Modeling and designing a PV system with DMPPT is remarkably more complex than implementing a standard MPPT technique. In this paper, a DMPPT system for PV arrays is proposed and analyzed. A dc and small-signal ac model is derived to analyze steady-state behavior, as well as dynamics and stability, of the whole system. Finally, simulation results are reported and discussed.

High-Performance Stand-Alone Photovoltaic Generation System

Abstract: This study develops a high-performance stand-alone photovoltaic (PV) generation system. To make the PV generation system more flexible and expandable, the backstage power circuit is composed of a high step-up converter and a pulsewidth-modulation (PWM) inverter. In the dc-dc power conversion, the high step-up converter is introduced to improve the conversion efficiency in conventional boost converters to allow the parallel operation of low-voltage PV arrays, and to decouple and simplify the control design of the PWM inverter. Moreover, an adaptive total sliding-mode control system is designed for the voltage control of the PWM inverter to maintain a sinusoidal output voltage with lower total harmonic distortion and less variation under various output loads. In addition, an active sun tracking scheme without any light sensors is investigated to make the PV modules face the sun directly for capturing the maximum irradiation and promoting system efficiency. Experimental results are given to verify the validity and reliability of the high step-up converter, the PWM inverter control, and the active sun tracker for the high-performance stand-alone PV generation system.

Dynamic Modeling and Control of a Grid-Connected Hybrid Generation System With Versatile Power Transfer

Abstract: This paper presents power-control strategies of a grid-connected hybrid generation system with versatile power transfer. The hybrid system is the combination of photovoltaic (PV) array, wind turbine, and battery storage via a common dc bus. Versatile power transfer was defined as multimodes of operation, including normal operation without use of battery, power dispatching, and power averaging, which enables grid- or user-friendly operation. A supervisory control regulates power generation of the individual components so as to enable the hybrid system to operate in the proposed modes of operation. The concept and principle of the hybrid system and its control were described. A simple technique using a low-pass filter was introduced for power averaging. A modified hysteresis-control strategy was applied in the battery converter. Modeling and simulations were based on an electromagnetic-transient-analysis program. A 30-kW hybrid inverter and its control system were developed. The simulation and experimental results were presented to evaluate the dynamic performance of the hybrid system under the proposed modes of operation.

Energy comparison of MPPT techniques for PV Systems

Abstract: Many maximum power point tracking techniques for photovoltaic systems have been developed to maximize the produced energy and a lot of these are well established in the literature. These techniques vary in many aspects as: simplicity, convergence speed, digital or analogical implementation, sensors required, cost, range of effectiveness, and in other aspects. This paper presents a comparative study of ten widely-adopted MPPT algorithms; their performance is evaluated on the energy point of view, by using the simulation tool Simulink®, considering different solar irradiance variations. Key-Words: - Maximum power point (MPP), maximum power point tracking (MPPT), photovoltaic (PV), comparative study, PV Converter.

An Adaptive System for Optimal Solar Energy Harvesting in Wireless Sensor Network Nodes

Abstract: The success of wireless sensor networks and their pervasive use is somehow constrained by energy supply which, generally provided by batteries, is a finite resource. Energy harvesting mechanisms must hence be taken into account to grant a long time operational life, with solar energy being the most interesting one in outdoor deployments due to its relatively high power density. In this paper we propose a low-power maximum power point tracker (MPPT) circuit specifically designed for wireless sensor nodes (hence effective, flexible, low cost and power-aware), i.e., a power transferring circuit for optimally conveying solar energy into rechargeable batteries even in not optimal weather conditions. High efficiency is granted by an ad hoc adaptive algorithm which, by keeping the MPPT electronics in its optimal working point, maximizes energy transfer from the solar cell to the batteries. The suggested implementation is particularly effective in critical weather conditions where traditional solutions do not work and is characterized by a flexible enough design for immediately hosting, in a plug in fashion, different solar panels and battery typologies.

Optimized Maximum Power Point Tracker for Fast-Changing Environmental Conditions

Abstract: This paper presents a high-performance maximum power point tracker (MPPT) optimized for fast cloudy conditions, e.g., rapidly changing irradiation on the photovoltaic panels. The rapidly changing conditions are tracked by an optimized hill-climbing MPPT method called dP-P&O. This algorithm separates the effects of the irradiation change from the effect of the tracker's perturbation and uses this information to optimize the tracking according to the irradiation change. The knowledge of the direction of the irradiation change enables the MPPT to use different optimized tracking schemes for the different cases of increasing, decreasing, or steady irradiance. When the irradiance is changing rapidly this strategy leads to faster and better tracking, while in steady-state conditions it leads to lower oscillations around the MPP. The simulations and experimental results show that the proposed dP-P&O MPPT provides a quick and accurate tracking even in very fast changing environmental conditions.

Renewable Energy Systems With Photovoltaic Power Generators: Operation and Modeling

Abstract: A substantial increase of photovoltaic (PV) power generators installations has taken place in recent years, due to the increasing efficiency of solar cells as well as the improvements of manufacturing technology of solar panels. These generators are both grid-connected and stand-alone applications. We present an overview of the essential research results. The paper concentrates on the operation and modeling of stand-alone power systems with PV power generators. Systems with PV array-inverter assemblies, operating in the slave-and-master modes, are discussed, and the simulation results obtained using a renewable energy power system modular simulator are presented. These results demonstrate that simulation is an essential step in the system development process and that PV power generators constitute a valuable energy source. They have the ability to balance the energy and supply good power quality. It is demonstrated that when PV array- inverters are operating in the master mode in stand-alone applications, they well perform the task of controlling the voltage and frequency of the power system. The mechanism of switching the master function between the diesel generator and the PV array-inverter assembly in a stand-alone power system is also proposed and analyzed. Finally, some experimental results on a practical system are compared to the simulation results and confirm the usefulness of the proposed approach to the development of renewable energy systems with PV power generators.

An Adaptive Solar Photovoltaic Array Using Model-Based Reconfiguration Algorithm

Abstract: This paper proposes an adaptive reconfiguration scheme to reduce the effect of shadows on solar panels. A switching matrix connects a solar adaptive bank to a fixed part of a solar photovoltaic (PV) array, according to a model-based control algorithm that increases the power output of the solar PV array. Control algorithms are implemented in real time. An experimental reconfiguration PV system with a resistive load is presented and is shown to verify the proposed reconfigurations.

A Maximum Power Point Tracking System With Parallel Connection for PV Stand-Alone Applications

Abstract: This paper presents the analysis, design, and implementation of a parallel connected maximum power point tracking (MPPT) system for stand-alone photovoltaic power generation. The parallel connection of the MPPT system reduces the negative influence of power converter losses in the overall efficiency because only a part of the generated power is processed by the MPPT system. Furthermore, all control algorithms used in the classical series-connected MPPT can be applied to the parallel system. A simple bidirectional dc-dc power converter is proposed for the MPPT implementation and presents the functions of battery charger and step-up converter. The operation characteristics of the proposed circuit are analyzed with the implementation of a prototype in a practical application.

Modeling and Optimization of a Solar Energy Harvester System for Self-Powered Wireless Sensor Networks

Abstract: In this paper, we propose a methodology for optimizing a solar harvester with maximum power point tracking for self-powered wireless sensor network (WSN) nodes. We focus on maximizing the harvester's efficiency in transferring energy from the solar panel to the energy storing device. A photovoltaic panel analytical model, based on a simplified parameter extraction procedure, is adopted. This model predicts the instantaneous power collected by the panel helping the harvester design and optimization procedure. Moreover, a detailed modeling of the harvester is proposed to understand basic harvester behavior and optimize the circuit. Experimental results based on the presented design guidelines demonstrate the effectiveness of the adopted methodology. This design procedure helps in boosting efficiency, allowing to reach a maximum efficiency of 85% with discrete components. The application field of this circuit is not limited to self-powered WSN nodes; it can easily be extended in embedded portable applications to extend the battery life.

Multilevel Diode-Clamped Converter for Photovoltaic Generators With Independent Voltage Control of Each Solar Array

Abstract: In photovoltaic (PV) power systems where a set of series-connected PV arrays (PVAs) is connected to a conventional two-level inverter, the occurrence of partial shades and/or the mismatching of PVAs leads to a reduction of the power generated from its potential maximum. To overcome these problems, the connection of the PVAs to a multilevel diode-clamped converter is considered in this paper. A control and pulsewidth-modulation scheme is proposed, capable of independently controlling the operating voltage of each PVA. Compared to a conventional two-level inverter system, the proposed system configuration allows one to extract maximum power, to reduce the devices voltage rating (with the subsequent benefits in device-performance characteristics), to reduce the output-voltage distortion, and to increase the system efficiency. Simulation and experimental tests have been conducted with three PVAs connected to a four-level three-phase diode-clamped converter to verify the good performance of the proposed system configuration and control strategy.

Long-Lifetime Power Inverter for Photovoltaic AC Modules

Abstract: This paper presents a power inverter tailored for low-power photovoltaic (PV) systems. The inverter features high reliability, thanks to a circuit topology that obviates aluminum electrolytic capacitors from the circuit. Moreover, all components, including logic and control, have been designed to exhibit high reliability at high temperatures. Three conversion stages form the power topology. First, a full bridge connected to a high-frequency transformer and a full-bridge rectifier amplifies the voltage of the PV panel to approximately 475 V. This stage is controlled by using a phase-shift pulsewidth-modulation controller that permits zero-voltage switching, thereby minimizing losses. Second, a buck converter is connected in series with the rectifier and is controlled by using current mode in order to shape the current injection into a rectified sine wave. Last, a full bridge is operated at line frequency to unfold the current injection. The amplification stage has a proportional compensator that maintains the voltage at the PV terminals constant. The current injection stage has a proportional-derivative compensator that controls the amplitude of the grid current so that the dc-link average voltage is maintained constant. Experimental results show that the peak efficiency of the system is 89%, and the total current harmonic distortion is below 5%. Finally, analyses show a designed lifetime of approximately ten years.

High-Performance Algorithms for Drift Avoidance and Fast Tracking in Solar MPPT System

Abstract: The power available at the output of solar arrays keeps changing with solar insolation and ambient temperature. Expensive and inefficient, the solar arrays must be operated at maximum power point (MPP) continuously for economic reasons. Of the numerous algorithms for this purpose, perturb and observe (P&O) is a standard. A derivative of gradient ascent method used in the optimization theory, this algorithm introduces a tradeoff between tracking and dynamic performance. This algorithm also has a tendency to drift the system away from the MPP as atmospheric conditions change. With continually changing atmospheric conditions, these inadequacies lead to poor utilization of solar arrays. This paper addresses both the issues. A variable-step-length algorithm is proposed to eliminate the tradeoff. The drift is minimized by evaluating the entire trend in a power versus voltage curve. Analytical results, validated on a prototype system show excellent performance.

Comparison of P&O and hill climbing MPPT methods for grid-connected PV converter

Abstract: Maximum power point tracking (MPPT) techniques are employed in photovoltaic (PV) systems to make full utilization of the PV array output power which depends on solar irradiation and ambient temperature. Among all the MPPT strategies, perturbation and observation (P&O) and hill climbing methods are widely applied in the MPPT controllers due to their simplicity and easy implementation. In this paper, both P&O and hill climbing methods are adopted to implement a grid-connected PV system. Their performance is evaluated and compared through theoretical analysis and digital simulation. P&O MPPT method exhibits fast dynamic performance and well regulated PV output voltage, which is more suitable than hill climbing method for grid-connected PV system.

Resistor Emulation Approach to Low-Power RF Energy Harvesting

Abstract: This paper presents an approach and associated circuitry for harvesting near maximum output power from electromagnetic waves in the RF/microwave region of the spectrum with variable incident power densities in the range of tens of muW/cm2. It is shown that open loop resistor emulation at the input port of a power converter is a suitable solution for tracking the peak power point of a low-power rectifying antenna source over a wide range of incident RF power densities. A boost converter with a simple low-power control approach for resistor emulation is presented. A hardware design example with detailed efficiency analysis is given using commercially available discrete circuitry. Experimental results are presented for a system harvesting 420 muW to 8 muW from a 6 cm times 6 cm rectifying antenna with incident RF power ranging from 70 muW/cm2 to 30 muW/cm2, respectively. The results demonstrate that resistor emulation is a simple and practical approach to energy harvesting with variable low-power radiative RF sources.

Optimum Design of the Current-Source Flyback Inverter for Decentralized Grid-Connected Photovoltaic Systems

Abstract: Two alternative modes of operation for the current-source flyback inverter are investigated in this paper. The discontinuous conduction mode (DCM), where a constant switching frequency (CSF) control method is applied, and the boundary between continuous and DCM (BCM) that is introduced for photovoltaic (PV) applications in this paper (where a variable switching frequency control method is applied). These two control methods are analytically studied and compared in order to establish their advantages as well as their suitability for the development of an inverter for decentralized grid-connected PV applications. An optimum design methodology is developed, aiming for an inverter with the smallest possible volume for the maximum power transfer to the public grid and wide PV energy exploitation. The main advantages of the current-source flyback inverter are very high-power density and high efficiency due to its simple structure, as well as high-power factor regulation. The design and control methodology are validated by personal computer simulation program with integrated circuit emphasis (PSPICE) simulation and experimental results, accomplished on a laboratory prototype.

A Single-Stage PV Module Integrated Converter Based on a Low-Power Current-Source Inverter

Abstract: This paper presents a transformerless three-phase inverter designed for the integration into a special type of a photovoltaic (PV) module, which is capable of providing an output voltage of several hundred volts. The chosen topology, a current-source inverter, features a single-stage power conversion system that directly feeds into the grid. The principle operation and control is described, and a modified modulation strategy is proposed to attenuate common-mode currents. A robust and highly efficient laboratory prototype of a 250-W module integrated converter has been implemented and tested. Its compact and flat design allows the direct attachment to the PV module.

MPPT techniques for PV Systems: Energetic and cost comparison

Abstract: In the future solar energy will be very important energy source. More than 45% of necessary energy in the world will be generated by photovoltaic array. Therefore it is necessary to concentrate our forces in order to reduce the application costs and to increment their performances. In order to reach this last aspect, it is important to note that the output characteristic of a photovoltaic array is nonlinear and changes with solar irradiation and the cellpsilas temperature. Therefore a maximum power point tracking (MPPT) technique is needed to draw peak power from the solar array in order to maximize the produced energy. This paper presents a comparative study of ten widely-adopted MPPT algorithms; their performance is evaluated using the simulation tool Simulinkreg. In particular, this study compares the behaviors of each technique in presence of solar irradiation variations.

Grid-Connected Photovoltaic Generation System

Abstract: This study addresses a grid-connected photovoltaic (PV) generation system. In order to make the PV generation system more flexible and expandable, the backstage power circuit is composed of a high step-up converter and a pulsewidth-modulation (PWM) inverter. In the dc-dc power conversion, the high step-up converter is introduced to improve the conversion efficiency of conventional boost converters and to allow the parallel operation of low-voltage PV modules. Moreover, an adaptive total sliding-mode control system is designed for the current control of the PWM inverter to maintain the output current with a higher power factor and less variation under load changes. In addition, an adaptive step-perturbation method is proposed to achieve the objective of maximum power point tracking, and an active sun tracking scheme without any light sensors is investigated to make PV plates face the sun directly in order to capture maximum irradiation and enhance system efficiency. Experimental results are given to verify the validity of the high step-up converter, the PWM inverter control, the ASP method, and the active sun tracker for a grid-connected PV generation system.

Efficient Charging of Supercapacitors for Extended Lifetime of Wireless Sensor Nodes

Abstract: This paper describes an efficient charging method for a supercapacitor-operated, solar-powered wireless sensor node called Everlast. Unlike traditional wireless sensors that store energy in batteries, Everlast's use of supercapacitors enables the system to operate for an estimated lifetime of 20 years without any maintenance. The novelty of this system lies in the feed-forward, pulse frequency modulated converter and open-circuit solar voltage method for maximum power point tracking (MPPT), enabling the solar cell to efficiently charge the supercapacitor and power the node. Experimental results show that by its low-complexity MPPT, Everlast can achieve over 89% conversion efficiency with lower power overhead than the state-of-the-art by two orders of magnitude, while enabling charging a supercapacitor up to 400% faster than direct charging. This makes Everlast particularly applicable to miniature-scale, high-impedance energy harvesting systems.

Optimized Maximum Power Point Tracker for fast changing environmental conditions

Abstract: This work presents a high performance Maximum Power Point Tracker (MPPT) optimized for fast cloudy conditions, e.g. rapidly changing irradiation on the PV panels. The rapidly changing conditions are tracked by an optimized hill-climbing MPPT method, called dP-P&O. This algorithm separates the effects of the irradiation change from the effect of the trackerpsilas perturbation, and uses this information to optimize the tracking according to the irradiation change. The knowledge of the direction of the irradiance change enables the MPPT to use different, optimized tracking schemes for the different cases of increase, decrease or steady irradiance. This strategy leads to faster and better tracking when the irradiance is changing rapidly, and lower oscillations around the MPP in steady-state conditions. The simulations and experimental results show that the proposed dP-P&O MPPT provides a quick and accurate tracking even in very fast changing environmental conditions.

Three-Phase Photovoltaic System With Three-Level Boosting MPPT Control

Abstract: This paper proposes a three-phase photovoltaic (PV) system with three-level boosting maximum power point tracking (MPPT) control. A simple MPPT control using a power hysteresis tracks the maximum power point (MPP), giving direct duty control for the three-level boost converter. The three-level boost converter reduces the reverse recovery losses of the diodes. Also, a weighted-error proportional and integral (PI) controller is suggested to control the dc link voltage faster. All algorithms and controllers were implemented on a single-chip microprocessor. Experimental results obtained on a 10-kW prototype show high performance, such as an MPPT efficiency (MPPT effectiveness) of 99.6%, a near-unity power factor, and a power conversion efficiency of 96.2%.

Development of a Methodology for Improving Photovoltaic Inverter Reliability

Abstract: In evaluating the energy-generation potential of a photovoltaic (PV) energy system, the system is usually assumed to work without interruptions over its entire life. PV energy systems are fairly reliable, but as any complex system, they may fail. In PV systems, the inverter is responsible for the majority of failures, and most inverter failures are blamed on the aluminum electrolytic capacitors typically used in the dc bus. This paper investigates the effects of common failure modes on the reliability of PV inverters and suggests a model framework for decomposing the inverter into subsystems for more detailed study. The challenges of statistical analysis based on small data sets are discussed, and simulations are performed to illustrate the proposed model using a simple decomposition into subsystems of the inverter used in the 342-kW PV system at the Georgia Tech Aquatic Center.