Showing papers on "Maximum power principle 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.

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.

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.

Efficiency at maximum power: An analytically solvable model for stochastic heat engines

Abstract: We study a class of cyclic Brownian heat engines in the framework of finite-time thermodynamics. For infinitely long cycle times, the engine works at the Carnot efficiency limit producing, however, zero power. For the efficiency at maximum power, we find a universal expression, different from the endoreversible Curzon-Ahlborn efficiency. Our results are illustrated with a simple one-dimensional engine working in and with a time-dependent harmonic potential.

Energy Scavenging From Low-Frequency Vibrations by Using Frequency Up-Conversion for Wireless Sensor Applications

Abstract: This paper presents an electromagnetic (EM) vibration-to-electrical power generator for wireless sensors, which can scavenge energy from low-frequency external vibrations. For most wireless applications, the ambient vibration is generally at very low frequencies (1-100 Hz), and traditional scavenging techniques cannot generate enough energy for proper operation. The reported generator up-converts low-frequency environmental vibrations to a higher frequency through a mechanical frequency up-converter using a magnet, and hence provides more efficient energy conversion at low frequencies. Power is generated by means of EM induction using a magnet and coils on top of resonating cantilever beams. The proposed approach has been demonstrated using a macroscale version, which provides 170 nW maximum power and 6 mV maximum voltage. For the microelectromechanical systems (MEMS) version, the expected maximum power and maximum voltage from a single cantilever is 3.97 muW and 76 mV, respectively, in vacuum. Power level can be increased further by using series-connected cantilevers without increasing the overall generator area, which is 4 mm2. This system provides more than an order of magnitude better energy conversion for 10-100 Hz ambient vibration range, compared to a conventional large mass/coil system.

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.

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.

Thermoelectric efficiency at maximum power in a quantum dot

Abstract: We identify the operational conditions for maximum power of a nanothermoelectric engine consisting of a single quantum level embedded between two leads at different temperatures and chemical potentials. The corresponding thermodynamic efficiency agrees with the Curzon-Ahlborn expression up to quadratic terms in the gradients, supporting the thesis of universality beyond linear response.

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%.

An Integrated Hybrid Power Supply for Distributed Generation Applications Fed by Nonconventional Energy Sources

Abstract: A new, hybrid integrated topology, fed by photovoltaic (PV) and fuel cell (FC) sources and suitable for distributed generation applications, is proposed. It works as an uninterruptible power source that is able to feed a certain minimum amount of power into the grid under all conditions. PV is used as the primary source of power operating near maximum power point (MPP), with the FC section (block), acting as a current source, feeding only the deficit power. The unique "integrated" approach obviates the need for dedicated communication between the two sources for coordination and eliminates the use of a separate, conventional dc/dc boost converter stage required for PV power processing, resulting in a reduction of the number of devices, components, and sensors. Presence of the FC source in parallel (with the PV source) improves the quality of power fed into the grid by minimizing the voltage dips in the PV output. Another desirable feature is that even a small amount of PV power (e.g., during low insolation), can be fed into the grid. On the other hand, excess power is diverted for auxiliary functions like electrolysis, resulting in an optimal use of the energy sources. The other advantages of the proposed system include low cost, compact structure, and high reliability, which render the system suitable for modular assemblies and "plug-n-play" type applications. All the analytical, simulation, and experimental results of this research are presented.

Modeling and Control of AWS-Based Wave Energy Conversion System Integrated Into Power Grid

Abstract: In this paper, the model of Archimedes wave swing (AWS) based wave energy conversion (WEC) system is proposed where a new coordinate transformation for the linear permanent magnet generator between the abc frame of reference and the dq0 frame of reference is proposed and the model of the LPMG in dq0 reference frame suitable for power system dynamic and stability analysis is derived for the first time. Since the output power and the induced voltage both vary, full-scale back-to-back converters are employed to connect the WEC to the power grid in order to maintain a constant active power and terminal voltage at the system side. The controllers for the generator side converter and the grid side converter of the back-to-back converters are also developed. Simulations are performed, when WEC operates under conditions such as no-load, supplying an isolated R-C load and integration with a power system, to simulate the dynamics of the WEC and verify the effectiveness of the model derived and the controllers developed. Comparison between the dynamic responses simulated and those obtained in the field test demonstrates that using the proposed dq0 model, the dynamics of the WEC system can be simulated properly. Using the generator side converter controller, the maximum power can be extracted from the wave while the loss in the LPMG can be minimized. Furthermore, the WEC can keep the output power at the power grid converter side constant and maintain the terminal voltage constant with the grid side converter controller. These are the desired features for the WEC to operate in parallel with the power grid. The effectiveness of the controller proposed is also validated under small disturbance.

Characterization of the harvesting capabilities of an ionic polymer metal composite device

Abstract: Harvesting systems capable of transforming dusty environmental energy into electrical energy have aroused considerable interest in the last two decades Several research works have focused on the transformation of mechanical environmental vibrations into electrical energy Most of the research activity refers to classic piezoelectric ceramic materials, but more recently piezoelectric polymer materials have been considered In this paper, a novel point of view regarding harvesting systems is proposed: using ionic polymer metal composites (IPMCs) as generating materials The goal of this paper is the development of a model able to predict the energy harvesting capabilities of an IPMC material working in air The model is developed by using the vibration transmission theory of an Euler?Bernoulli cantilever IPMC beam The IPMC is considered to work in its linear elastic region with a viscous damping contribution ranging from 01 to 100?Hz An identification process based on experimental measurements performed on a Nafion? 117 membrane is used to estimate the material parameters The model validation shows a good agreement between simulated and experimental results The model is used to predict the optimal working region and the optimal geometrical parameters for the maximum power generation capacity of a specific membrane The model takes into account two restrictions The first is due to the beam theory, which imposes a maximum ratio of 05 between the cantilever width and length The second restriction is to force the cantilever to oscillate with a specific strain; in this paper a 03% strain is considered By considering these two assumptions as constraints on the model, it is seen that IPMC materials could be used as low-power generators in a low-frequency region The optimal dimensions for the Nafion? 117 membrane are length = ?12?cm and width = ?62?cm, and the electric power generation is 3?nW at a vibrating frequency of 709?rad?s?1 IPMC materials can sustain big yield strains, so by increasing the strain allowed on the material the power will increase dramatically, the expected values being up to a few microwatts

A New Maximum Power Point Tracking for Photovoltaic Systems

Abstract: In this paper a new maximum power point tracking algorithm for photovoltaic arrays is proposed. The algorithm detects the maximum power point of the PV. The computed maximum power is used as a reference value (set point) of the control system. ON/OFF power controller with hysteresis band is used to control the operation of a Buck chopper such that the PV module always operates at its maximum power computed from the MPPT algorithm. The major difference between the proposed algorithm and other techniques is that the proposed algorithm is used to control directly the power drawn from the PV. The proposed MPPT has several advantages: simplicity, high convergence speed, and independent on PV array characteristics. The algorithm is tested under various operating conditions. The obtained results have proven that the MPP is tracked even under sudden change of irradiation level. Keywords—Photovoltaic, maximum power point tracking, MPPT.

Efficiency of molecular motors at maximum power

Abstract: Molecular motors transduce chemical energy obtained from hydrolizing ATP into mechanical work exerted against an external force. We calculate their efficiency at maximum power output for two simple generic models and show that the qualitative behaviour depends crucially on the position of the transition state or, equivalently, on the load distribution factor. Specifically, we find a transition state near the initial state (sometimes characterized as a "power stroke") to be most favorable with respect to both high power output and high efficiency at maximum power. In this regime, driving the motor further out of equilibrium by applying higher chemical potential differences can even, counterintuitively, increase the efficiency.

Integrated Doubly Fed Electric Alternator/Active Filter (IDEA), a Viable Power Quality Solution, for Wind Energy Conversion Systems

Abstract: In response to electric energy crisis and power quality concerns, a simple and low-cost variable speed integrated doubly fed electric alternator/active filter (IDEA) for wind energy conversion systems is proposed. The proposed IDEA is capable of simultaneously capturing maximum power of wind energy with fluctuating wind speed and improving power quality, which are achieved by canceling the most significant and troublesome harmonics of the utility grid. Power factor correction and reactive power control are the other two significant features of the proposed technology. The back-to-back current-regulated power converters are employed to excite the rotor of IDEA. The control strategy of rotor side power converter is based on position sensorless field oriented control method with higher power density. A laboratory prototype has been fabricated and tested, and a TMS3202407 DSP-based controller has been used to control the back-to-back power converters. Analysis and experimental results are presented to demonstrate the effectiveness of the proposed integrated IDEA.

Dynamic Models of Wind Turbines

Abstract: The impact of wind power generation in the power system is no longer negligible. Therefore, there is an urgent need for wind turbine models that are capable of accurately simulating the interaction between wind turbines or wind farms and the power system. One problem is that no standardized model of wind turbines for power system stability studies is currently available. In response to this problem, generic dynamic models of wind turbines for stability studies are proposed in this thesis. Three wind turbine concepts are considered; fixed-speed wind turbines (FSWTs), doubly fed induction generator (DFIG) wind turbines and full converter wind turbines (FCWTs). The proposed models are developed for positive-sequence phasor time-domain dynamic simulations and are implemented in the standard power system simulation tool PSS/E with a 10 ms time step. Response accuracy of the proposed models is validated against detailed models and, in some cases, against field measurement data. A direct solution method is proposed for initializing a DFIG wind turbine model. A model of a dc-link braking resistor with limited energy capacity is proposed, thus a unified model of an FCWT for a power system stability analysis can be obtained. The results show that the proposed models are able to simulate wind turbine responses with sufficient accuracy. The generic models proposed in this thesis can be seen as a contribution to the ongoing discourse on standardized models of wind power generation for power system stability studies. Aggregated models of wind farms are studied. A single equivalent unit representation of a wind farm is found to be sufficient for most short-term voltage stability investigations. The results show that non-linearities due to maximum power tracking characteristics and saturation of electrical controllers play no important role in characterizing wind farm responses. For a medium-term study, which may include wind transport phenomena, a cluster representation of a wind farm provides a more realistic prediction. Different influencing factors in designing dynamic reactive power compensation for an offshore wind farm consisting of FSWTs are also investigated. The results show that fault ride-through capability of the individual turbines in the wind farm utilizing an active stall control significantly reduces the requirement for the dynamic reactive power compensation.

Distributed maximum power point tracking converter

Abstract: The present system and method provides a maximum power point tracking converter for use with a solar cell group in a distributed manner within a solar panel. According to one embodiment, one or more solar cells within a solar panel are grouped and coupled to a distributed converter that extracts maximum power from the coupled solar cell group.

Method and apparatus for maximum power point tracking in power conversion based on dual feedback loops and power ripples

Abstract: A method and apparatus for converting DC input power to AC output power. The apparatus comprises a conversion module comprising an input capacitor, and a first feedback loop for determining a maximum power point (MPP) and operating the conversion module proximate the MPP. The apparatus additionally comprises a second feedback loop for determining a difference in energy storage and delivery by the input capacitor, producing an error signal indicative of the difference, and coupling the error signal to the first feedback loop to adjust at least one operating parameter of the conversion module to drive toward the MPP.

Efficiency of molecular motors at maximum power

Abstract: Molecular motors transduce chemical energy obtained from hydrolizing ATP into mechanical work exerted against an external force. We calculate their efficiency at maximum power output for two simple generic models and show that the qualitative behaviour depends crucially on the position of the transition state. Specifically, we find a transition state near the initial state (sometimes characterized as a "power stroke") to be most favorable with respect to both high power output and high efficiency at maximum power. In this regime, driving the motor further out of equilibrium by applying higher chemical potential differences can even, counter-intuitively, increase the efficiency.

Analysis of perturb and observe maximum power point tracking algorithm for photovoltaic applications

Abstract: This paper highlights the compromises between good steady-state accuracy and the speed of convergence in Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm. Three fixed step-sizes and a variable step-size have been defined as the perturbation step-sizes and the effect of applying different step-sizes for P&O algorithm are discussed. The perturbation step-sizes have been simulated using Matlab/Simulink and the maximum power tracking efficiency for each step-size is analysed. These step-sizes have been experimentally tested using a PV illumination test rig to emulate rapid changes in shadow effect on a PV panel. The fixed step-sizes are tested using a direct duty-cycle control boost converter while the variable step-size is examined by applying current-mode controlled boost converter. It is concluded that the application of fixed perturbation step-size has a limitation in performing MPPT while a variable step-size is necessary to balance the competing aims of speed and accuracy.

High efficiency remotely controllable solar energy system

Abstract: A solar energy system (55) has aspects that can allow individualized control and analysis for overall field power control that can be used while harvesting maximum power from a solar energy source (1) and a string of solar panels (11) for a power grid (10). The invention provides control of power at high efficiency with aspects that can exist independently including: 1) power management with switch disconnect control (64), 2) sequenced start of a solar power system, 3) providing a safety output system that can be handled by installers and maintenance and advantageously controlled, 4) providing programmable power functionality controller (86) either on site or remotely from an administrative facility by radio transmission individual solar panel disconnect control (85), 5) a system with pattern analyzer (87) for operational, installation, and maintenance indications, and 6) systems with individual solar panel string power simulator (89) for disparate components.

Energy harvesting from motion using rotating and gyroscopic proof masses

Abstract: Energy harvesting — the extraction of energy from the local environment for conversion to electrical power — is of particular interest for low power wireless devices such as body or machine mounted sensors. Motion and vibration are a potential energy source, and can be exploited by inertial devices, which derive electrical power by the damping of the relative movement of a proof mass mounted in a frame attached to the moving host. Inertial devices using linear motion of the proof mass, which have been extensively studied and developed, have a maximum power output limited by the internal travel range of the proof mass. In the current paper, the potential power of devices using rotating proof masses, powered by linear or rotational host motion, is analysed. Two new operation modes are introduced: rotationally resonant devices, and devices driven by continuous rotation. In each case the maximum achievable power densities are estimated, and these are compared with equivalent expressions for devices with linea...