Showing papers on "Rotor (electric) published in 2009"

Wind energy explained : theory, design, and application

Abstract: Preface Acknowledgements Introduction: Modern wind energy and its origins Modern wind turbines History of wind energy Wind characteristics and resources Introduction General characteristics of the wind resource Characteristics of the atmospheric boundary layer Wind data analysis and resource estimation Wind turbine energy production estimates using statistical techniques Overview of available resource assessment data Wind measurements and instrumentation Advanced topics Aerodynamics of wind turbines General overview One-dimensional momentum theory and the Betz limit Ideal horizontal axis wind turbing with wake rotation' Airfoils and general concepts of aerodynamics Momentum theory and blade element theory Blade shape for ideal rotor without wake rotation General rotor blade shape performance prediction Blade shape for optimum rotor with wake rotation Generalized rotor design procedure Simplified HAWT rotor performance calculation procedure Effect of drag and blade number on optimum performance Advanced aerodynamic topics Mechanics and dynamics Wind turbine rotor dynamics Detailed and specialized dynamic models Electrical aspects of wind turbines Basic concepts of electric power Power transformers Electrical machines Power converters Ancillary electrical equipment Wind turbine design Design procedure Wind turbine topologies Materials Machine elements Wind turbine loads Wind turbine subsystems and components Design evaluation Power curve prediction Wind turbine loads Wind turbine subsystems and components Design evaluation Power curve prediction Wind turbine control Overview of wind turbine control systems Typical grid-connected turbine operation Supervisory control overview and implementation Dynamic control theory and implementation Wind turbine siting, system design and integration Wind turbine siting Installation and operation issues Wind farms Wind turbines and wind farms in electric grids Offshore wind farms Operation in severe climates Hybrid electrical systems Wind energy system economics Overview of economic assessment of wind energy systems Capital costs of wind energy systems Operation and maintenance costs Value of wind energy Economic analysis methods Wind energy market considerations Wind energy systems: environmental aspects and impacts Avian interaction with wind trubines Visual impact of wind turbines Wind turbine noise Electromagnetic interference effects Land-use environmental impacts Other environmental considerations Nomenclature Problems Index

Ride Through of Wind Turbines With Doubly Fed Induction Generator Under Symmetrical Voltage Dips

Abstract: This paper deals with the grid fault ride-through capability of doubly fed induction generators. These machines are very sensitive to grid disturbances. To prevent the damages that voltage dips can cause on the converter, most machines are equipped nowadays with a crowbar that short circuits the rotor. However, during the crowbar activation, the rotor converter must be disconnected, hence the power generated with the turbine is no longer controlled. In doing so, the crowbar impedes the wind turbine from carrying out the voltage stabilization required by most new grid codes. This paper proposes a novel control strategy that notably reduces the crowbar activation time. As a result, the control of the turbine might shortly be resumed and the turbine can furthermore supply a reactive power fulfilling the newest grid regulations. Experimental results of a complete system are included, demonstrating the viability of the proposed control.

Modeling of a variable speed wind turbine with a Permanent Magnet Synchronous Generator

Abstract: The aim of this work is to analyze a typical configuration of a Wind Turbine Generator System (WTGS) equipped with a Variable Speed Generator. Nowadays, doubly-fed induction generators are being widely used on WTGS, although synchronous generators are being extensively utilized too. There are different types of synchronous generators, but the multi-pole Permanent Magnet Synchronous Generator (PMSG) is chosen in order to obtain its model. It offers better performance due to higher efficiency and less maintenance since it does not have rotor current and can be used without a gearbox, which also implies a reduction of the weight of the nacelle and a reduction of costs. Apart from the generator, the analyzed WTGS consists of another three parts: wind speed, wind turbine and drive train. These elements have been modeled and the equations that explain their behavior have been introduced. What is more, the whole WTGS has been implemented in MATLAB/Simulink interface. Moreover, the concept of the Maximum Power Point Tracking (MPPT) has been presented in terms of the adjustment of the generator rotor speed according to instantaneous wind speed.

Grid tied converter with virtual kinetic storage

Abstract: The increase of relatively small scale dispersed power generation (DG) is likely to impact the structure and operation of power generation and distribution systems. The current power system comprises multiple generators. Their intrinsic kinetic energy buffer (rotor inertia) plays an important role in short term system stability. Generators that are connected via power electronic power converters lack these kinetic buffers. Optimal power transfer from source to grid is often used as a control objective to optimize the energy yield. At power system level this approach may compromise stability. In this paper it is demonstrated that by emulation of rotor inertia, stability problems on a system level can be mitigated. For that purpose a short-term energy buffer is added to the system that can be controlled at a fast rate, thereby forming a so-called Virtual Synchronous Generator (VSG). Power system stability support then becomes an additional control objective of the DG. Maximum rotor angular speed deviation and maximum critical clearing time are used as performance indicators for the evaluation. Sizing of the short term buffer constitutes a second topic of this paper.

Hybrid Terminal Sliding-Mode Observer Design Method for a Permanent-Magnet Synchronous Motor Control System

Abstract: This paper proposes a hybrid terminal sliding-mode observer based on the nonsingular terminal sliding-mode (NTSM) and the high-order sliding-mode (HOSM) for the rotor position and speed estimation in the permanent-magnet synchronous motor control system. An NTSM manifold is utilized to realize both fast convergence and better tracking precision. In addition, a derivative estimator is used to obtain the derivative of the sliding-mode function. Meanwhile, an HOSM control law is designed to guarantee the stability of the observer and eliminate the chattering, so that smooth back-electromotive-force (EMF) signals can be obtained without a low-pass filter. According to the back-EMF equations, the rotor position and speed of the motor can be calculated. Simulation and experimental results are presented to validate the proposed method.

Analysis of heat conduction in a disk brake system

Abstract: In this paper, the governing heat equations for the disk and the pad are extracted in the form of transient heat equations with heat generation that is dependant to time and space. In the derivation of the heat equations, parameters such as the duration of braking, vehicle velocity, geometries and the dimensions of the brake components, materials of the disk brake rotor and the pad and contact pressure distribution have been taken into account. The problem is solved analytically using Green’s function approach. It is concluded that the heat generated due to friction between the disk and the pad should be ideally dissipated to the environment to avoid decreasing the friction coefficient between the disk and the pad and to avoid the temperature rise of various brake components and brake fluid vaporization due to excessive heating.

Sensorless Maximum Power Point Tracking of Wind by DFIG Using Rotor Position Phase Lock Loop (PLL)

Abstract: This paper presents an invention, the rotor position phase lock loop (PLL), which enables maximum power point (MPPT) tracking of wind by doubly-fed induction generators without needing a tachometer, an absolute position encoder, or an anemometer. The rotor position PLL is parameter variation insensitive, requiring only an estimate of the magnetization inductance for it to operate. It is also insensitive to noise in the electrical measurements. Proof of concept is by: (1) digital simulations and (2) experimental testing of a laboratory prototype.

Feedback–feedforward individual pitch control for wind turbine load reduction

Abstract: This paper focuses on the problem of wind turbine fatigue load reduction by means of individual pitch control (IPC). The control approach has a two-degree-of-freedom structure, consisting of an optimal multivariable LQG controller and a feedforward disturbance rejection controller based on estimated wind speed signals. To make the control design problem time invariant, all signals are transformed to the non-rotating reference frame using the Coleman transformation. In the Coleman domain, the LQG control objective is minimization of the rotor tilt and yaw moments, whereas the feedforward controller tries to achieve even further improvement by rejecting the influence of the low-frequency components of the wind on the rotor moments. To this end, the tilt- and yaw-oriented components of the blade-effective wind speeds are approximated using stochastic random walk models, the states of which are then augmented with the turbine states and estimated using a Kalman filter. The effects of these (estimated) disturbances on the controlled outputs are then reduced using stable dynamic model inversion. The approach is tested and compared with the conventional IPC method in simulation studies with models of different complexities. The results demonstrate very good load reduction at not only low frequencies (1p blade fatigue load reduction) but also at the 3p frequency, giving rise to fatigue load reduction of the non-rotating turbine components. Copyright © 2008 John Wiley & Sons, Ltd.

Wind turbine rotor-tower interaction using an incompressible overset grid method

Abstract: In this paper, 3D Navier–Stokes simulations of the unsteady flow over the NREL Phase VI turbine are presented. The computations are carried out using the structured grid, incompressible, finite volume flow solver EllipSys3D, which has been extended to include the use of overset grids. Computations are presented, firstly, on an isolated rotor, and secondly, on the downwind configuration of the turbine, which includes modelling of the rotor, tower and tunnel floor boundary. The solver successfully captures the unsteady interaction between the rotor blades and the tower wake, and the computations are in good agreement with the experimental data available. The interaction between the rotor and the tower induces significant increases in the transient loads on the blades and is characterized by an instant deloading and subsequent reloading of the blade, associated with the velocity deficit in the wake, combined with the interaction with the shed vortices, which causes a strongly time-varying response. Finally, the results show that the rotor has a strong effect on the tower shedding frequency, causing under certain flow conditions vortex lock-in to take place on the upper part of the tower. Copyright © 2009 John Wiley & Sons, Ltd.

A comparison of smart rotor control approaches using trailing edge flaps and individual pitch control

Abstract: Modern wind turbines have been steadily increasing in size, and have now become very large, with recent models boasting rotor diameters greater than 120 m. Reducing the loads experienced by the wind turbine rotor blades is one means of lowering the cost of energy of wind turbines. Wind turbines are subjected to signiflcant and rapid ∞uctuating loads, which arise from a variety of sources including: turbulence in the wind, tower shadow, wind shear, and yawed ∞ow conditions. \Smart rotor control" concepts have emerged as a major topic of research in the attempt to reduce fatigue loads on wind turbines. In this approach, aerodynamic load control devices are distributed along the span of the wind turbine blade, and through a combination of sensing, control, and actuation, these devices dynamically control the loads on the blades. This research investigates the load reduction potential of smart rotor control devices, namely trailing edge ∞aps (TEFs), in the operation of a 5 MW wind turbine in the aeroelastic design code \GH Bladed." Speciflcally in this paper, the fatigue load reductions achieved using trailing edge ∞aps are evaluated, and the performance is compared to another promising load reduction technique, individual pitch control. A feedback control approach is implemented for load reduction, which utilizes a multiblade coordinate transformation, so that variables in the rotating frame of reference can be mapped into a flxed frame of reference. Single input single output (SISO) control techniques for linear time invariant (LTI) systems are then employed to determine the appropriate response of the TEFs based on the loads on the blades. The use of TEFs and this control approach is shown to efiectively reduce the fatigue loads on the blades, relative to a baseline controller. The load reduction potential is also compared to an alternative individual pitch control approach, in the time and frequency domain. The efiects on the pitch and power systems are brie∞y evaluated, and the limitations of the analysis are assessed.

Shape Optimization of Wind Turbine Blades

Abstract: This paper presents a design tool for optimizing wind turbine blades. The design model is based on an aerodynamic/aero-elastic code that includes the structural dynamics of the blades and the Blade Element Momentum (BEM) theory. To model the main aero-elastic behaviour of a real wind turbine, the code employs 11 basic degrees of freedom corresponding to 11 elastic structural equations. In the BEM theory, a refined tip loss correction model is used. The objective of the optimization model is to minimize the cost of energy which is calculated from the annual energy production and the cost of the rotor. The design variables used in the current study are the blade shape parameters, including chord, twist and relative thickness. To validate the implementation of the aerodynamic/aero-elastic model, the computed aerodynamic results are compared to experimental data for the experimental rotor used in the European Commision-sponsored project Model Experiments in Controlled Conditions, (MEXICO) and the computed aero-elastic results are examined against the FLEX code for flow past the Tjaereborg 2 MW rotor. To illustrate the optimization technique, three wind turbine rotors of different sizes (the MEXICO 25 kW experimental rotor, the Tjaereborg 2 MW rotor and the NREL 5 MW virtual rotor) are applied. The results show that the optimization model can reduce the cost of energy of the original rotors, especially for the investigated 2 MW and 5 MW rotors. Copyright © 2009 John Wiley & Sons, Ltd.

Impact of MMF Space Harmonic on Rotor Losses in Fractional-Slot Permanent-Magnet Machines

Abstract: The fractional-slot permanent-magnet (PM) machines are used in many applications due to their high torque density, low torque ripple, and high efficiency. However, the fractional-slot machines are characterized by high contents of space harmonics in the air-gap MMF distribution. Such harmonics cause flux variation in the air gap, and the main consequence is the induced losses in the rotor. Depending on the combination of slots and poles of the machine, there are different harmonic contents and then rotor losses. By means of a simple model of the rotor losses, this paper investigates the link between the rotor losses and the combination of the slots and the poles of the fractional-slot PM machines.

Drive device for vehicle

Abstract: A vehicle driving apparatus is provided which can execute cranking of an internal combustion engine by transmitting a mechanical power from a rotor of a motor to an engine output shaft without executing an engaging/disengaging operation of a clutch. A driving apparatus 10 of a hybrid vehicle 1 includes a first speed change mechanism 30 capable of receiving the mechanical power from an engine output shaft 8 by a first input shaft 27 and transmitting the mechanical power to drive wheels 88, a second speed change mechanism 40 capable of receiving the mechanical power from the engine output shaft 8 and a rotor 52 by a second input shaft 28 engaged with the rotor 52 and transmitting the mechanical power to the drive wheels 88, a first clutch 21 capable of engaging the engine output shaft 8 with the first input shaft 27, and a second clutch 22 capable of engaging the engine output shaft 8 with the second input shaft 28, wherein the second clutch 22 is placed in an engaged state when operation force for executing an engaging/disengaging operation is not applied to the second clutch 22.

Online Detection of Broken Rotor Bars in Induction Motors by Wavelet Packet Decomposition and Artificial Neural Networks

Abstract: We present an algorithm for the online detection of rotor bar breakage in induction motors through the use of wavelet packet decomposition (WPD) and neural networks. The system provides a feature representation of multiple frequency resolutions for faulty modes and accurately differentiates between healthy and faulty conditions, and its main applicability is to dynamic time-variant signals experienced in induction motors during run time. The algorithm analyzes rotor bar faults by WPD of the induction motor stator current. The extracted features with different frequency resolutions, together with the slip speed, are then used by a neural network trained for the detection of faults. The experimental results show that the proposed method is able to detect the faulty conditions with high accuracy.

Intact flagellar motor of Borrelia burgdorferi revealed by cryo-electron tomography: evidence for stator ring curvature and rotor/C-ring assembly flexion.

Abstract: The bacterial flagellar motor is a remarkable nanomachine that provides motility through flagellar rotation. Prior structural studies have revealed the stunning complexity of the purified rotor and C-ring assemblies from flagellar motors. In this study, we used high-throughput cryo-electron tomography and image analysis of intact Borrelia burgdorferi to produce a three-dimensional (3-D) model of the in situ flagellar motor without imposing rotational symmetry. Structural details of B. burgdorferi, including a layer of outer surface proteins, were clearly visible in the resulting 3-D reconstructions. By averaging the 3-D images of approximately 1,280 flagellar motors, a approximately 3.5-nm-resolution model of the stator and rotor structures was obtained. flgI transposon mutants lacked a torus-shaped structure attached to the flagellar rod, establishing the structural location of the spirochetal P ring. Treatment of intact organisms with the nonionic detergent NP-40 resulted in dissolution of the outermost portion of the motor structure and the C ring, providing insight into the in situ arrangement of the stator and rotor structures. Structural elements associated with the stator followed the curvature of the cytoplasmic membrane. The rotor and the C ring also exhibited angular flexion, resulting in a slight narrowing of both structures in the direction perpendicular to the cell axis. These results indicate an inherent flexibility in the rotor-stator interaction. The FliG switching and energizing component likely provides much of the flexibility needed to maintain the interaction between the curved stator and the relatively symmetrical rotor/C-ring assembly during flagellar rotation.

“Active Flux” DTFC-SVM Sensorless Control of IPMSM

Abstract: This paper proposes an implementation of a motion-sensorless control system in wide speed range based on "active flux" observer, and direct torque and flux control with space vector modulation (DTFC-SVM) for the interior permanent magnet synchronous motor (IPMSM), without signal injection. The concept of "active flux" (or "torque producing flux") turns all the rotor salient-pole ac machines into fully nonsalient-pole ones. A new function for Lq inductance depending on torque is introduced to model the magnetic saturation. Notable simplification in the rotor position and speed estimation is obtained, because the active flux position is identical with the rotor position. Extensive experimental results are presented to verify the principles and to demonstrate the effectiveness of the proposed sensorless control system. With the active flux observer, the IPMSM drive system operates from very low speed of 2 r/min at half full-load up to 1400 r/min. Higher speed is possible, in principle, with flux weakening.

Direct Virtual Torque Control for Doubly Fed Induction Generator Grid Connection

Abstract: This paper presents a grid-connection control strategy of doubly fed induction generator wind system based on the direct control of both a virtual torque and rotor flux of the generator. This control is achieved with no proportional-integral regulator and requires the measurement of only grid voltages, rotor currents, and rotor position. The same switching table is used for grid synchronization and for running process. A field-programmable-gate-array-based design of the proposed control is developed and tested on a 4-kW experimental prototype. Experimental results are provided to show the effectiveness of the fast and soft grid-connection method developed.

Demagnetization Analysis of Permanent Magnets According to Rotor Types of Interior Permanent Magnet Synchronous Motor

Abstract: This paper shows a study on the demagnetization performance analysis of permanent magnet according to three kinds of rotor types of an interior permanent magnet synchronous motor (IPMSM). It is very important to consider demagnetization performance as well as motor performance such as rated torque, output current, and efficiency when designing IPMSM. Three kinds of rotor types according to permanent magnet arrangement; single layer type, v shape type, and double layer type are generally used for IPMSM. In the paper, the magnetic equivalent circuits according to each rotor type are proposed in order for initial design of thickness of permanent magnets considering demagnetization by lumped constant related to magnetic circuit. The volume of permanent magnets per pole and back EMF of each rotor type is assumed to equal for the comparison of demagnetization of IPMSMs with same performance each other. Next, distribution of demagnetization in the permanent magnet is analyzed by using finite element method (FEM) for the verification of the results by magnetic equivalent circuit.

Loss Analysis of Permanent-Magnet Motors With Concentrated Windings—Variation of Magnet Eddy-Current Loss Due to Stator and Rotor Shapes

Abstract: In this paper, we investigate losses, including magnet eddy-current loss of permanent-magnet synchronous motors with concentrated windings. A 3-D finite-element method that considers carrier harmonics of pulsewidth modulation inverters is utilized to calculate the losses in each part of the motor separately. A simple linear magnetic circuit model is also introduced in order to understand the mechanism of eddy-current loss generation in the magnet. First, the measured and calculated results are compared to verify the validity of the analysis. Next, the variation of the losses due to the stator and rotor shapes is investigated, for instance, concentrated and distributed stator windings and interior and surface-mounted permanent magnets. It is clarified that the eddy-current loss of the permanent magnet in the concentrated winding motor is much larger than that in the distributed winding motor. The difference of the loss generation mechanism due to the rotor shape is also clarified.

Variable magnetic flux electric rotary machine

Abstract: An electric rotary machine is disclosed which can adjust relative angles of sub-rotors continuously and regardless of torque direction without generating an attractive force between the field magnets of the sub-rotors The electric rotary machine includes: a stator having a winding; a dual rotor which is rotatably disposed with a gap from the stator and divided axially along a shaft into a first rotor and a second rotor each having field magnets with different polarities arranged alternately in a rotation direction; a mechanism for varying the axial position of the second rotor relative to the first rotor continuously; and a non-magnetic member located between the first rotor and the second rotor

Prognostic Health Management of Aircraft Power Generators

Abstract: In this paper, prognostic tools are developed to detect the onset of electrical failures in an aircraft power generator, and to predict the generator's remaining useful life (RUL). Focus is on the rotor circuit since failure mode, effects, and criticality analysis (FMECA) studies indicate that it is a high priority candidate for condition monitoring. A signature feature is developed and tested by seeded fault experiments to verify that the initial stages of rotor faults are observable under diverse generator load conditions. A tracking filter is used to assess the damage state and predict generator RUL. This information helps to avoid unexpected failures while reducing the overall life-cycle cost of the system.

Rotating electrical machine

Abstract: PROBLEM TO BE SOLVED: To provide a rotating electrical machine, capable of suppressing generation of eddy current loss due to a harmonic components of an electric current and capable of improving the strength of a rotor. SOLUTION: The rotating electrical machine 1 has a stator 2 and a rotor 3 rotatable with respect to the stator 2. The rotor 3 has a rotor core 7 formed from a plurality of sheets 7a piled up axially and a plurality of permanent magnets 8 formed on the rotor core 7. A plurality of welds number limit areas 12, surrounding a rotor core 7 circumferentially along the rotor core 7, are arranged axially in line around the outer-peripheral portion of the rotor core 7. In each of the plurality of welds number limit areas 12, the number of circumferential welds of the rotor core 7 is identical to that of the pairs of poles of the rotor 3. Furthermore, the welds in the welds number limit areas 12 adjacent to each other are arranged, being shifted circumferentially along the rotor core 7. COPYRIGHT: (C)2010,JPO&INPIT

Hovering aerial vehicle with removable rotor arm assemblies

Abstract: The invention provides a hovering aerial vehicle with removable rotor arms and protective shrouds. Removing the shrouds reduces the weight of the vehicle and increases flight time. Removing the rotor arms makes the vehicle easier to transport. Removable rotor arms also simplify field repair or replacement of damaged parts.

Multiobjective Optimal Design for Interior Permanent Magnet Synchronous Motor

Abstract: This paper presents a method on a multiobjective optimal design of interior permanent magnet synchronous motor (IPMSM) with V-shaped permanent magnet rotor for high performance. In general, a design method adopting equivalent magnetic circuit is used for basic design of IPMSM. However, its use may give us wrong design result because of air-gap flux calculation method by using lumped reluctance parameters. Moreover, it has difficulty in considering arrangement of permanent magnets and barriers, but on the other hand, there exists high degree of freedom of permanent magnet rotor design of IPMSM. Therefore, finite element method (FEM) is needed for the precise design considering arrangement of permanent magnets and barriers. In order for effective V-shaped permanent magnet rotor design, Taguchi method by adopting five multiobjective functions is proposed as an optimal design method. The different optimal design results are suggested by adjusting weighting value of each objective function. Finally, the characteristics of optimal design model with V-shaped permanent magnet rotor are verified by experiment.

Prediction of wind turbine noise and validation against experiment

Abstract: A semi-empirical prediction method for trailing edge noise is applied to calculate the noise from two modern large wind turbines. The prediction code only needs the blade geometry and the turbine operating conditions as input. Using detailed acoustic array and directivity measurements, a thorough validation of the predictions is carried out. The predicted noise source distribution in the rotor plane (as a function of frequency and observer position) shows the same characteristics as in the experiments: due to trailing edge noise directivity and convective amplification, practically all noise (emitted to the ground) is produced during the downward movement of the blades, causing an amplitude modulation of broadband aerodynamic blade noise at the blade passing frequency ('swish'). Good agreement is also found between the measured and predicted spectra, in terms of levels and spectral shape. For both turbines, the deviation between predicted and measured overall sound levels (as a function of rotor power) is...