Showing papers on "Maximum power principle published in 2003"

Comparative study of maximum power point tracking algorithms

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

A study on a two stage maximum power point tracking control of a photovoltaic system under partially shaded insolation conditions

Abstract: A photovoltaic (PV) array shows relatively low output power density, and has a greatly drooping current-voltage (I-V) characteristic. Therefore, maximum power point tracking (MPPT) control is used to maximize the output power of the PV array. Many papers have been reported in relation to MPPT. However, the current-power (I-P) curve sometimes shows multilocal maximum points mode under nonuniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output point which is not the real maximal output point on the I-P curve. Some papers have been also reported, trying to avoid this difficulty. However most of those control systems become rather complicated. Then, the two stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under nonuniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and Lab VIEW.

Controlling power consumption of at least one computer system

Abstract: At least one computer system receives power from a power system having a maximum power output based on a nominal power consumption of the at least one computer system. The power system is operable to detect an amount of power consumed by the at least one computer system, and compare the power consumption to a threshold based on the maximum power output of the power supply. The power system is operable to place one or more components of the at least one computer system in a lower-power state to reduce power consumption in response to the amount of power consumed by the at least one computer system exceeding the threshold.

A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter

Abstract: A novel technique for efficiently extracting the maximum output power from a solar panel under varying meteorological conditions is presented. The methodology is based on connecting a pulse-width-modulated (PWM) DC/DC SEPIC or Cuk converter between a solar panel and a load or battery bus. The converter operates in discontinuous capacitor voltage mode whilst its input current is continuous. By modulating a small-signal sinusoidal perturbation into the duty cycle of the main switch and comparing the maximum variation in the input voltage and the voltage stress of the main switch, the maximum power point (MPP) of the panel can be located. The nominal duty cycle of the main switch in the converter is adjusted to a value, so that the input resistance of the converter is equal to the equivalent output resistance of the solar panel at the MPP. This approach ensures maximum power transfer under all conditions without using microprocessors for calculation. Detailed mathematical derivations of the MPP tracking technique are included. The tracking capability of the proposed technique has been verified experimentally with a 10-W solar panel at different insolation (incident solar radiation) levels and under large-signal insolation level changes.

Method and apparatus for preventing overloads of power distribution networks

Abstract: Systems and methods for monitoring power in power distribution systems are provided. In one aspect, a system for monitoring power includes a power monitoring device that measures a value of at least one characteristic of power provided to a branch of a power distribution system. The power monitoring device includes an output that provides the value measured. The system further includes a controller having an input to receive the value measured and an output that couples to a first device powered by the branch to send a maximum power signal to the first device to command the first device to operate at a percentage of maximum power.

Conditioning circuit for a power supply at the maximum power point, a solar generator, and a conditioning method

Abstract: The invention relates to a conditioning circuit that measures operating points of a power supply to deduce therefrom the current-voltage characteristic thereof and to determine directly the voltage corresponding to its maximum power point, without using any kind of tracking algorithm that causes the operating point of the power unit to oscillate about the maximum power point The maximum power point voltage VMPP is supplied to a controller which regulates a power cell by slaving it to the input voltage until the output voltage of the supply is equal to the maximum power point voltage V MPP The invention also relates to a solar generator and an associated conditioning method One particular application is to high-power satellites

Income, Wealth, and the Maximum Principle

Abstract: Preface Introduction Part I. Introduction to the Maximum Principle 1. The Calculus of Variations and the Stationary Rate of Return on Capital 2. The Prototype-Economic Control Problem 3. The Maximum Principle in One Dimension 4. Applications of the Maximum Principle in One Dimension Part II. Comprehensive Accounting and the Maximum Principle 5. Optimal Multisector Growth and Dynamic Competitive Equilibrium 6. The Pure Theory of Perfectly Complete National Income Accounting 7. The Stochastic Wealth and Income Version of the Maximum Principle References Index

Maximum power point tracking of coupled inductor interleaved boost converter supplied PV system

Abstract: A photovoltaic generator exhibits nonlinear voltage-current characteristics and its maximum power point varies with solar radiation. A two-cell interleaved boost converter with coupled inductors is used to match the photovoltaic system to the load and to operate the solar cell array at maximum power point. A maximum power point tracking algorithm is developed using only load voltage information, eliminating the array current detection. The present converter system has the advantages of low ripple content, both on the load and source side, improved efficiency and reduced switch stress, as compared to noncoupled two-cell interleaved converters. As a result, a lower value of array capacitance is sufficient for smoothing the array voltage and current. Analytical expressions for the photovoltaic source and interleaved boost converter, corresponding to maximum power point operation of the SCA, are derived. Experimental results are presented to demonstrate the suitability of this converter system. Few experimental observations are also presented for partial shading conditions. Further, a comparative study of coupled and noncoupled interleaved boost converters for photovoltaic applications is made. These studies reveal that, by introducing coupling among the parallel branch inductors, it is possible to improve steady-state performance while maintaining the dynamic performance of the photovoltaic system.

Performance analysis of an irreversible quantum heat engine working with harmonic oscillators.

Abstract: The cycle model of a regenerative quantum heat engine working with many noninteracting harmonic oscillators is established. The cycle consists of two isothermal and two constant-frequency processes. The performance of the cycle is investigated, based on the quantum master equation and semigroup approach. The inherent regenerative losses in the two constant-frequency processes are calculated. The expressions of several important performance parameters such as the efficiency, power output, and rate of the entropy production are derived for several interesting cases. Especially, the optimal performance of the cycle in high-temperature limit is discussed in detail. The maximum power output and the corresponding parameters are calculated. The optimal region of the efficiency and the optimal ranges of the temperatures of the working substance in the two isothermal processes are determined.

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

Abstract: 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.

Long-term operational experience with first Siemens 400 kW HTS machine in diverse configurations

Abstract: Siemens has built a synchronous machine consisting of an HTS rotor and an air-cored stator. Rotor cooling is provided by a Gifford-McMahon (GM) "off the shelf" cryocooler, the typical requirement being about 30 W @ 25 K. The machine was designed for a rated power of 380 kW (rated voltage 3 phases 400 V Y), but achieved a maximum continuous power of 450 kW and a short term maximum power of 590 kW at 1500 rpm. In all cases, output power was limited by stator cooling. Characteristic parameters such as reactances, inductances, and time constants were determined to obtain a consistent overview of the machine properties. The machine was tested under different operational modes, including motor mode as well as generator mode. In the generator mode, it was operated on water cooled resistors or connected to the grid. The properties of motor mode have been determined synchronized to the grid as well as via an inverter. Special attention was taken to investigate the influences of asymmetric loads, grid and inverter harmonics on rotor cooling requirements. Numerical calculations were performed and compared to the experimental data showing good correlation.

Electric-energy generation using variable-capacitive resonator for power-free LSI: efficiency analysis and fundamental experiment

Abstract: A power generator based on a vibration-to-electric energy converter using a variable-resonating capacitor is experimentally demonstrated. The generator consists of a complete system with a mechanical variable capacitor, a charge-transporting LC tank circuit and an externally powered timing-capture controller. A practical design methodology to maximize the efficiency of the vibration-to-electric energy generation system is also described. The efficiency of the generator is estimated based on three factors: the mechanical-energy loss, the charge-transportation loss, and the timing-capture loss. Through the mechanical-energy analysis, the optimum condition for the resonance is found. The parasitic elements in the charge transporter and the timing management of the capture scheme dominate the generation efficiency. These analyses enable the optimum design of the energy-generation system. An experimentally fabricated and measured generator theoretically has a maximum power of 580 nW; the measured power is 120 nW, so conversion efficiency is 21%. This results from a 43% mechanical energy loss and a 63% charge-transportation loss. The timing-capture scheme is manually determined and externally powered in the experiment, so its efficiency is not considered. With our result, a new system LSI application with an embedded power source can be explored for the ubiquitous computing era.

The theoretical limits to the power output of a muscle–tendon complex with inertial and gravitational loads

Abstract: When a muscle delivers power to an inertial load through a spring, the peak power can exceed the maximum that the muscle alone could produce. Using normalized differential equations relating dimensionless quantities we show, by solving the equations either analytically or numerically, that one dimensionless constant (Xi), representing the inertial load, is sufficient to specify the behaviour during shortening of a muscle-tendon complex with linear force-velocity and force-extension properties. In the presence of gravity, an additional constant (Gamma), representing the gravitational acceleration, is required. Nonlinear force-velocity and force-extension relationships each introduce an additional constant, representing their curvature. In the absence of gravity the power output delivered to an inertial load is limited to approximately 1.4 times the maximum power of the muscle alone, and when gravity is present the power delivered is limited to approximately twice the power of muscle alone. These limits are found for the purely inertial load at Xi ca. 1 and with gravity acting at XiGamma = 0.5 with Xi arbitrarily small. The effects of nonlinear muscle and tendon properties tend to cancel each other out and do not produce large deviations from these optima. A lever system of constant ratio between muscle and load does not alter these limits. Cams and catches are required to exceed these limits and attain the high power outputs sometimes observed during explosive animal movement.

Sensorless variable-speed controller for existing fixed-speed wind power generator with unity-power-factor operation

Abstract: A variable-speed controller, for an existing 225 kW fixed-speed wind power generator, is presented in this paper. A sensorless direct torque control algorithm-based controller is proposed for the squirrel-cage induction generator. Generator torque reference is derived based on sensorless maximum power tracking mode algorithm, up to the base speed of the generator. A three-phase front-end converter is used here to deliver the generated power to the grid with unity-power-factor operation at all wind speeds. This algorithm is based on direct active and reactive power control. The experimental waveforms from the actual installation site are presented in this paper with a comparison of the existing fixed-speed system. An interpretation of the results is also presented here.

Maximum power generation in a piezoelectric pulse generator

Abstract: This investigation presents and discusses maximization techniques for a high-power piezoelectric pulse generator. Maximizing the piezoelectric generator's output power is done by maximizing the product of generated voltage and output current. The maximization methods are derived from the mechanical and electrical models of the generator and provide design guidelines as to the geometric dimensions of the piezoelectric material and circuital conditions that will produce maximum power in the device. The theoretical results show the peak stack voltage to increase with an increasing thickness to area ratio of the piezoelectric material and with increasing applied force. However, in contrast to the peak output voltage, the peak output current increases with the decreasing of thickness to area ratio of the material. In addition to the physical dimension, the peak stack current increases as the value of the antenna inductor decreases. The output power of the piezoelectric generator, which is the product of output voltage and current, linearly increases with the thickness to area ratio. This result is due to the fact that the output voltage is larger comparing to the output current. Experimental results are also given to verify the theoretical results and represent the performance of several types of piezoelectric materials with different thickness to area ratios. The experimental results show good agreement with theoretical predictions. The results also show the peak power output of the experimental generator ranging from 7 to 28 kW with a corresponding power density from 9 to 173 kW/cm/sup 3/.

Method and configuration for controlling a wind energy installation without a gearbox by electronically varying the speed

Abstract: The electronic generator power P G is compared with a predetermined power range in order to set the torque of the synchronous generator of a wind energy installation. A choice between two control modes is made on the basis of the comparison, and a reference power P G * is determined that corresponds to the maximum power production. This reference power P G * is compared with the electrical generator power P G , and a reference current I E * that is proportional to the power difference is produced and supplied to the field controller. The field controller draws power in a controlled manner from the capacitive DC voltage intermediate circuit as a function of the reference current I E *, and supplies this power to the excitation field. Changing the excitation field results in a change in the torque and hence in the rotational speed of the synchronous generator, which enables the two power values to be matched.

A simplified nonlinear power source for simulating PV panels

Abstract: Power electronic converters play a major role in the efficiency and reliability of photovoltaic (PV) systems. The development of power conditioning equipment for operation at the maximum power point and for utility interfacing usually requires solar array simulators (SAS) that are relatively expensive. This paper presents a simple nonlinear power source based on a PWM switched resistor that can be used for preliminary evaluations of power conditioning equipment for PV systems. It presents V/spl times/I characteristics similar to those of PV panels and also allows the variation of the solar irradiation level. The operating principles are discussed, design equations are derived and experimental results are presented for a 75 Wp PV panel simulator.

Current control loop for tracking of maximum power point supplied for photovoltaic array

Abstract: A novel method is used for projecting and implementing a current control loop as a means for regulating the power flow originated of a photovoltaic generator, based on three-phase nonautonomous static converter dc-ac functioning as an inverter. The maximum efficiency is the main issue presented in this work. A strategy for tracking the maximum power point (MMPT) for several solar insolation levels has been used in this paper. The control loop circuit, a three-phase nonautonomous static converter dc-ac, operating as inverter, is experimentally mounted to verify the proposed control strategy performance. Since the characteristic volt-ampere of a photovoltaic array depends on solar cell temperature, on sunshine incident, and on load, it is very difficult to achieve an optimum matching at all insolation levels and at all temperature variations. In this work the temperature effect will be neglected, since in our region (north of Brazil), the temperature remains approximately constant, around 30 degrees Celsius. In this regard, the temperature variations will be neglected.

Solar-array modelling and maximum power point tracking using neural networks

Abstract: This paper is studying a solar-array modelling and maximum power point tracking by comparing 2 neural networks which are back-propagation neural network and radial basis function neural network. Neural network has the potential to provide an improved method of deriving nonlinear models which is complementary to conventional techniques. The performance of the models and predicted maximum power point of solar cell are evaluated by comparing it with that of the conventional model by simulation. The simulation results has shown that both neural network work very well. In addition, the simulation results have shown that training for back-propagation takes longer time than radial basis function. However, back-propagation neural network needs less information for training. Radial basis function needs more information in order to get accurate modelling.

State-based power analysis for systems-on-chip

Abstract: Early power analysis for systems-on-chip (SoC) is crucial for determining the appropriate packaging and cost. This early analysis commonly relies on evaluating power formulas for all cores for multiple configurations of voltage, frequency, technology and application parameters, which is a tedious and error-prone process. This work presents a methodology and algorithms for automating the power analysis of SoCs. Given the power state machines for individual cores, this work defines the product power state machine for the whole SoC and uses formal symbolic simulation algorithms for traversing and computing the minimum and maximum power dissipated by sets of power states in the SoC.

Stand-alone photovoltaic energy storage system with maximum power point tracking

Abstract: This digests deals with the study of a stand-alone photovoltaic system, which is able to extract the maximum power from photovoltaic array for all solar intensity conditions and to provide output voltage regulation. The proposed system consists of a DC-DC converter in combination with battery energy storage in a simple structure. Operating principle and control strategy are described. Digital simulation is included, supporting the validity of the concept.

Performance Modeling of a Piezo-Hydraulic Actuator

Abstract: A simple quasi-static model has been developed as an engineering tool for improving the performance of a piezo-hydraulic actuator's fluid system. The model's predictions compare reasonably well with experimental data at low frequencies (<150 Hz) as trends in the dependence of actuation speed on driving frequency and applied load are captured within 30%. The model indicates that there is an optimum load and driving frequency that corresponds to maximum power output but that the operating conditions for optimum power output and efficiency are different. The efficiency of the fluid system decreases with increasing frequency at a rate that depends on the load. Viscous losses through the valves and tubing are negligible compared with the inertial losses associated with accelerating and decelerating the load. This acceleration and deceleration process occurs twice per piezo cycle because of the configuration of the fluid system used to rectify the oscillatory motion of the piezo stack. Accordingly, the inertia ...

On Some Nonendoreversible Engine Models with Nonlinear Heat Transfer Laws

Abstract: In this work, we analyze a nonendoreversible thermal engine model with a nonlinear heat transfer law between the heat reservoirs and the working fluid under two optimization criteria: the maximum power regime and the so-called ecological criterion. We find that this nonendoreversible model has a similar behaviour to that shown by De Vos (Am. J. Phys. 53, 570 (1985)) for endoreversible models with two thermal conductances with only one superior conductance and with only one inferior conductance, respectively. The model is compared with two sets of real power plants, the first one containing power plants of old design (before 1960's) and the second one being formed by modern nuclear power plants. Our results suggest that the first group was designed under conditions which, are reminiscent of a maximum power regime and the second one under an ecological-like criterion. We also study some general properties of nonendoreversible thermal engine models.

Electric device and method for operating an electric device

Abstract: An electric device features a two-wire interface which two-wire interface serves to feed electric power to the electric device and also to transmit a signal, with the maximum power drawn via the two-wire interface in normal operation being restricted to a predefined upper limit. The permissible maximum power consumption of the electric device is automatically and temporarily increased beyond the predefined upper limit when the electric device is switched into a special operational function mode. The length of time in which the electric device is in the special operational function mode can thus be reduced.

Independently sourced parallel-connected power systems with maximum power tracking

Abstract: The paper presents a multiple-channel distributed maximum power tracking (MPT) power system with channel outputs connected in parallel, and channel inputs connected to independent power sources. A "shared-bus" current-sharing method utilizing the distributed MPT control system is well suited to regulate parallel-connected current-mode DC-DC converters dedicated to each power channel. For broader applications with distributed solar-array sources, the distributed MPT approach was implemented to achieve robust stability. The approach was successfully validated through a two-channel 1500 W prototype, yielding nearly uniform current-sharing and reliable MPT performance. Each power channel was shown to track the array peak power from 50 W to 600 W with tracking efficiency of nearly 100%. The multiple-channel distributed-MPT power system provides ease of power expansion, stable current-sharing, fault-tolerance, and autonomous MPT control.

Power dissipation analysis in tapping-mode atomic force microscopy

Abstract: In a tapping-mode atomic force microscope, a power is dissipated in the sample during the imaging process. While the vibrating tip taps on the sample surface, some part of its energy is coupled to the sample. Too much dissipated power may mean the damage of the sample or the tip. The amount of power dissipation is related to the mechanical properties of a sample such as viscosity and elasticity. In this paper, we first formulate the steady-state tip-sample interaction force by a simple analytical expression, and then we derive the expressions for average and maximum power dissipated in the sample by means of sample parameters. Furthermore, for a given sample elastic properties we can determine approximately the sample damping constant by measuring the average power dissipation. Simulation results are in close agreement with our analytical approach.

Optimization on the performance of a harmonic quantum Brayton heat engine

Abstract: The cycle model of an irreversible quantum heat engine working with many noninteracting harmonic oscillators is established. The engine cycle consists of two adiabatic and two constant-frequency processes and is referred to as the harmonic quantum Brayton cycle. The general performance characteristics of the cycle are investigated, based on the quantum master equation and semigroup approach. Expressions for several important performance parameters, such as the efficiency, power output, and rate of the entropy production, are derived. By using numerical solutions, the power output of the heat engine subject to finite cycle duration is optimized. The maximum power output and the corresponding parameters are calculated numerically. The optimal regions of the efficiency and the optimal ranges of temperatures of the working substance and times spent on the two constant-frequency processes are determined. Moreover, the optimal performance of the cycle in the high-temperature limit is compared with that of a classical Brayton heat engine working with an ideal gas. The results obtained here show that in the high-temperature limit, a harmonic quantum Brayton cycle may be equivalent to a classical Brayton cycle.

Power supply control device for controlling the power supply to a multiplicity of electric loads in a motor vehicle, applies priorities to different loads and maintains stable supply to vital loads

Abstract: A device for operating and controlling a large number of electrical loads in a motor vehicle that are supplied by an electrical power supply (102). An energy calculation device determines the amount of available power, while a priority changing device assigns priorities to the various electrical loads on the bases of input information relating to the motor vehicle state. A command device generates command values that govern the maximum power to be supplied to each load, based on the priorities. Thus the total power use is kept within the available power limit.