Showing papers on "Rotor (electric) published in 2004"

Comparison of the response of doubly fed and fixed-speed induction generator wind turbines to changes in network frequency

Abstract: Synchronous and fixed-speed induction generators release the kinetic energy of their rotating mass when the power system frequency is reduced. In the case of doubly fed induction generator (DFIG)-based wind turbines, their control system operates to apply a restraining torque to the rotor according to a predetermined curve with respect to the rotor speed. This control system is not based on the power system frequency and there is negligible contribution to the inertia of the power system. A DFIG control system was modified to introduce inertia response to the DFIG wind turbine. Simulations were used to show that with the proposed control system, the DFIG wind turbine can supply considerably greater kinetic energy than a fixed-speed wind turbine.

Electrical Insulation for Rotating Machines: Design, Evaluation, Aging, Testing, and Repair

Abstract: Preface.1. Rotating Machine Insulation Systems.2. Evaluating Insulation Materials and Systems.3. Historical Development of Insulation Materials and Systems.4. Stator Winding Insulation Systems in Current Use.5. Rotor Winding Insulation Systems.6. Core Laminations and Their Insulation.7. General Principles of Winding Failure, Repair and Rewinding.8. Stator Failure Mechanisms and Repair.9. Rotor Winding Failure Mechanisms and Repair.10. Core Lamination Insulation Failure and Repair.11. General Principles of Testing and Monitoring.12. Off-Line Rotor and Stator Winding Tests.13. In-Service Monitoring of Stator and Rotor Windings.14. Core Testing.15. Acceptance and Site Testing of New Windings.16. Maintenance Strategies.Index.About the Authors.

Speed regulator for a brushless dc motor

Abstract: Speed regulator for a brushless DC motor, wherein the DC motor comprises a stator, a rotor and an electromagnet wherein the electromagnet is in the vicinity of the stator, the rotor produces a permanent magnetic field and the electromagnet is activated to generate an alternating magnetic field; furthermore comprising a power supply and a regulating element, the regulating element being connected to the power supply to regulate the power feed to the electromagnet, so that, during use, a torque generated by the DC motor is regulated, characterised in that the speed regulator is able to generate a voltage V(φ) as a function of rotor speed of revolution, rotor position (φ), rotor load and motor activation, wherein the speed regulator sets the change in the voltage V(φ) of the motor as a function of the rotor position φ in such a way that the instantaneous torque T(φ), at least in the vicinity of the reversal in polarity of the driving magnetic field, complies with the conditions that the derivative (φ)/∂φ is essentially zero and the second derivative ∂2T(φ)/∂φ2 is an essentially monotonic function.

Sensorless vector control of induction machines for variable-speed wind energy applications

Abstract: A sensorless vector-control strategy for an induction generator in a grid-connected wind energy conversion system is presented. The sensorless control system is based on a model reference adaptive system (MRAS) observer to estimate the rotational speed. In order to tune the MRAS observer and compensate for the parameter variation and uncertainties, a separate estimation of the speed is obtained from the rotor slot harmonics using an algorithm for spectral analysis. This algorithm can track fast dynamic changes in the rotational speed, with high accuracy. Two back-to-back pulse-width-modulated (PWM) inverters are used to interface the induction generator with the grid. The front-end converter is also vector controlled. The dc link voltage is regulated using a PI fuzzy controller. The proposed sensorless control strategy has been experimentally verified on a 2.5-kW experimental set up with an induction generator driven by a wind turbine emulator. The emulation of the wind turbine is performed using a novel strategy that allows the emulation of high-order wind turbine models, preserving all of the dynamic characteristics. The experimental results show the high level of performance obtained with the proposed sensorless vector-control method.

Influence of the variable-speed wind generators in transient stability margin of the conventional generators integrated in electrical grids

Abstract: This work demonstrates that the integration of variable-speed wind systems with doubly fed induction generators (DFIG) and a four-quadrant AC-to-AC converter connected to the rotor windings increases the transient stability margin of the electrical grids, when compared with the case where the fixed speed wind systems with cage generators are used. It is due to the influence of the two dedicated rotor current regulators of the DFIG on the dynamic behavior of the other generators in the system. Besides, adequate models to represent the behavior of the DFIG in transient stability studies are presented. From the simulation results, some important conclusions can be extracted to guide the integration of the wind farms on weak or strong grids.

Rotor Eddy-Current Loss in Permanent-Magnet Brushless AC Machines

Abstract: This paper analyzes rotor eddy-current loss in permanent-magnet brushless ac machines. It is shown that analytical or finite-element techniques published in literature for predicting rotor eddy-current loss using space harmonic based approaches may not yield correct results in each magnet segment when one magnet-pole is circumferentially segmented into more than two pieces. It is also shown that the eddy-current loss in each equally segmented piece may differ by a large margin, which implies that the temperature distribution in the magnets will be uneven and the risk of demagnetization has to be carefully assessed. The theoretical derivation is validated by time-stepped transient finite-element analysis.

Handbook of Rotordynamics

Abstract: Keywords: rotor ; vibration ; rotation ; dynamique Reference Record created on 2005-11-18, modified on 2016-08-08

Low-cost sensorless control of brushless DC motors with improved speed range

Abstract: This paper presents a low-cost position sensorless control scheme for brushless dc motors. Rotor position information is extracted by indirectly sensing the back EMF from only one of the three motor-terminal voltages for a three-phase motor. Depending on the terminal voltage sensing locations, either a low-pass filter or a band-pass filter is used for position information retrieval. This leads to a significant reduction in the component count of the sensing circuit. The cost saving is further increased by coupling the sensing circuit with a single-chip microprocessor or digital signal processor for speed control. In addition, a look-up-table-based correction for the nonideal phase delay introduced by the filter is suggested to ensure accurate position detection even at low speed. This extends the operating speed range and improves motor efficiency. Experimental results are included to verify the proposed scheme.

Inductance model-based sensorless control of the switched reluctance motor drive at low speed

Abstract: A sensorless control scheme for the switched reluctance motor (SRM) drive at low speed is presented in this paper. The incremental inductance of each active phase is estimated using the terminal measurement of this phase. The estimated phase incremental inductance is compared to an analytical model, which represents the functional relationships between the phase incremental inductance, phase current, and rotor position, to estimate the rotor position. The presented sensorless control scheme requires neither extra hardware nor huge memory space for implementation. It can provide accurate rotor position information even as the magnetic characteristics of the SRM change due to aging. Combined with other inductance model-based sensorless control techniques, the proposed method can be used to develop an inductance model-based sensorless control scheme to run the SRM from standstill to high-speed. Simulation and experimental results are presented to verify the proposed scheme.

Application of direct drive wheel motor for fuel cell electric and hybrid electric vehicle propulsion system

Abstract: This paper presents a gearless wheel motor drive system specifically designed for fuel cell electric and hybrid electric vehicle propulsion application. The system includes a liquid-cooled axial flux permanent-magnet machine designed to meet the direct-drive requirements. The machine design implements techniques to increase the machine inductance in order to improve machine constant power range and high-speed efficiency. The implemented technique reduces machine spin loss to further improve efficiency. The machine design also optimizes the placement of magnets in the rotor to reduce cogging and ripple torque. An original cooling system arrangement based on the use of high thermal conductivity epoxy joining machine stator and liquid-cooled aluminum casing allows the very effective removal of machine power loss. Design details and experimental results are presented

Methods and apparatus for rotor blade ice detection

Abstract: A method for detecting ice on a wind turbine having a rotor and one or more rotor blades each having blade roots includes monitoring meteorological conditions relating to icing conditions and monitoring one or more physical characteristics of the wind turbine in operation that vary in accordance with at least one of the mass of the one or more rotor blades or a mass imbalance between the rotor blades. The method also includes using the one or more monitored physical characteristics to determine whether a blade mass anomaly exists, determining whether the monitored meteorological conditions are consistent with blade icing; and signaling an icing-related blade mass anomaly when a blade mass anomaly is determined to exist and the monitored meteorological conditions are determined to be consistent with icing.

Motor driving apparatus

Abstract: A motor driving apparatus comprises an inverter circuit for converting an output voltage of a power supply into a three-phase AC and outputting the same to the brushless motor; a rotor position estimation unit for estimating a rotor position of the brushless motor; and an inverter control unit for controlling the inverter circuit so that the brushless motor is driven by a current based on the estimated rotor position. The inverter control unit determines an advance angle of the current supplied to the brushless motor with respect to the estimated rotor position so as to minimize a deviation between a command rpm and an actual rpm. Therefore, it is possible to perform stable weak field control for the brushless motor, independently from the input voltage of the inverter circuit, without using predetermined control variables such as table values.

Models for bearing damage detection in induction motors using stator current monitoring

Abstract: This paper describes new models for the influence of rolling-element bearing faults on induction motor stator current. Bearing problems are one major cause for drive failures. Their detection is possible by vibration monitoring of characteristic bearing frequencies. As it is possible to detect other machine faults by monitoring the stator current, a great interest exists in applying the same method for bearing fault detection. After a presentation of the existing fault model, a new detailed approach is proposed. It is based on two effects of a bearing fault: the introduction of a particular radial rotor movement and load torque variations caused by the bearing fault. The theoretical study results in new expressions for the stator current frequency content. Experimental tests with artificial and realistic bearing damage were conducted by measuring vibration, torque and stator current. The obtained results by spectral analysis of the measured quantities validate the proposed theoretical approach.

Methods for Increasing Region 2 Power Capture on a Variable-Speed Wind Turbine

Abstract: The standard region 2 control scheme for a variable-speed wind turbine,t c5Kv 2 , has several shortcomings that can result in significant power loss. The first of these is that there is no accurate way to determine the gain K; modeling programs are not accurate enough to represent all of the complex aerodynamics, and these aerodynamics change over time. Furthermore, it is not certain whether the value of K used in the standard control even provides for the maximum energy capture under real-world turbulent conditions. We introduce new control methods to address these issues. First, we show in simulation that using smaller values of K than the standard can result in increased energy capture. Second, we give simulation results showing that an optimally tracking rotor control scheme can improve upon the standard scheme by assisting the rotor speed in tracking wind-speed fluctuations more rapidly. Finally, we propose an adaptive control scheme that allows for maximum power capture despite parameter uncertainty. @DOI: 10.1115/1.1792653#

Online rotor mixed fault diagnosis way based on spectrum analysis of instantaneous power in squirrel cage induction motors

Abstract: Broken rotor bars and eccentricity are common faults in squirrel cage induction motors. These two faults usually occur simultaneously. This paper will deal with this kind of mixed fault. It is well known that the characteristic frequency of broken bars in the stator line current of a squirrel cage induction motor is very near to that of the fundamental component. In the spectrum of the stator line current, the characteristic components related to broken rotor bars are always submerged by the fundamental one, and it is difficult to detect the broken bar fault at an early stage. In our work, instantaneous power of the motor is used as the quantity to be monitored. Theoretical analysis indicates that the spectrum of ac level of the spectrum of the instantaneous power is clear from any component at the fundamental supply frequency, and the fault characteristics can be highlighted, which is effective toward the separation of mixed faults and the quantification of the fault extent. Experimental results have demonstrated the effectiveness of the proposed technique.

Optimized Permanent Magnet Generator Topologies for Direct-Drive Wind Turbines

Abstract: The thesis deals with the issue of cost reduction in direct-drive generators for wind turbines. Today, the combination gearbox-medium-speed (1000-2000 rpm) induction generator largely dominates the market of MW-scale wind turbines. This is due to the lower costs of the gearbox option compared to the costs of gearless systems. Nevertheless, there is an acute interest among researchers and wind turbine suppliers in the possibility of removing gears and slip rings from the drive train, leading to lower maintenance (no oil is required and slip rings can be avoided) and higher reliability due to the absence of wear between gears. The direction followed by the thesis is the investigation and comparison of various permanent magnet (PM) machine topologies. The aim is to identify the topology(ies) with the lowest cost/torque and highest torque/ mass. A new TFPM geometry, called TFPM machine with toothed rotor, is derived in the. The new machine topology has the following characteristics: the stator is single-sided, the rotor PM and flux concentrators are independent from the build-up of mechanical tolerances, the installation of rotor parts (PM and flux concentrators) can be automated and the flux circulation allows laminated steel to be used in the stator core. A prototype of the TFPM machine with toothed rotor is presented. The comparison between TFPM machines with toothed rotor and conventional PM synchronous machines is discussed. Comparison of the cost/torque and torque/mass of the two machine topologies for diameters ranging between 0.5 m and 3.0 m showed favorable expected performances of the TFPM machine with toothed rotor for diameters of 0.5 m and 1.0 m. However, diameters larger than 1.0 m favored the conventional PM synchronous machine with/without flux-concentration. Using the results of the optimization process, the costs of active material are computed for a 1.5 MW wind turbine. It is found that active material represents about 5% of the total turbine cost, while previous estimates indicated that the generator costs are rather between 30% and 40% of a complete direct-drive wind turbine. Therefore, further optimiza¬tion of direct-drive machines should also include the costs of manufacturing and the costs of the mechanical structure.

Control system for doubly fed induction generator

Abstract: A controller (28) for a doubly fed induction generator (12, 20) adjusts control signals to a rotor side converter (24) and line side converter (22) to adjust rotor current when a voltage transient on a utility grid (10) occurs, so that the doubly fed induction generator can ride through the transient. The controller can also turn off the transistors of the rotor side converter (24) to reduce rotor current and/or activate a crowbar (42) to reduce the voltage of the DC link (26) connecting the converters (22, 24) when significant voltage transients occur on the grid (10). This permits continued operation of the DFIG system without disconnecting from the grid.

Compact high power alternator

Abstract: An apparatus for converting between mechanical and electrical energy, particularly suited for use as a compact high power alternator for automotive use and “remove and replace” retrofitting of existing vehicles. The apparatus comprises a rotor with permanent magnets, a stator with a winding, and a cooling system. Mechanisms to prevent the rotor magnets from clashing with the stator by minimizing rotor displacement, and absorbing unacceptable rotor displacement are disclosed. The cooling system directs coolant flow into thermal contact with at least one of the winding and magnets, and includes at least one passageway through the stator core. Various open and closed cooling systems are described. Cooling is facilitated by, for example, loosely wrapping the winding end turns, use of an asynchronous airflow source, and/or directing coolant through conduits extending through the stator into thermal contact with the windings.

Three-Dimensional Multi-Objective Design Optimization of a Transonic Compressor Rotor

Abstract: A method for transonic compressor multi-objective design optimization was developed and applied to the NASA rotor 37, a test case representative of complex three-dimensional viscous flow structures in transonic bladings. The optimization problem considered was to maximize the isentropic efficiency of the rotor and to maximize its pressure ratio at the design point, using a constraint on the mass flow rate. The three-dimensional Navier‐Stokes code CFXTASCflow ® was used for the aerodynamic analysis of blade designs. The capability of the code was validated by comparing the computed results to experimental data available in the open literature from probe traverses upand downstream of the rotor. A multi-objective evolutionary algorithm was used for handling the optimization problem that makes use of Pareto optimality concepts and implements a novel genetic diversity evaluation method to establish a criterion for fitness assignment. The optimal rotor configurations, which correspond to the maximum pressure ratio and maximum efficiency, were obtained and compared to the original design.

Power smoothing in wind generation systems using a sensorless vector controlled induction Machine driving a flywheel

Abstract: This paper presents a novel control strategy for power smoothing in generation systems in which power flow variations can occur. These variations are the norm in wind energy generation. The system is based on a sensorless vector controlled induction machine driving a flywheel. The induction machine is controlled to operate in a wide speed range by using flux weakening above rated speed. A speed observer is used to obtain the rotational speed in the whole speed range. In order to tune the speed observer and compensate for the parameter variation and uncertainties, a separate estimation of the speed is obtained from the rotor slot harmonics using an algorithm for spectral analysis. This algorithm can track fast dynamic changes in the rotational speed, with high accuracy. The control strategies have been experimentally verified on a 3.5-kW experimental setup with an induction machine and flywheel. The experimental results show the high level of performance obtained with the proposed sensorless vector control system.

Electrical machine with double-sided stator

Abstract: Machines useful for wind turbine and ship propulsion purposes include a wind turbine generator or a ship propulsion motor with two concentric air gaps. In one embodiment, the machine includes a rotor with an inner rotor core and an outer rotor core; and a double-sided stator with an inner stator side and an outer stator side. The double-sided stator is concentrically disposed between the inner rotor core and the outer rotor core.

A thermodynamic analysis of different options to break 60% electric efficiency in combined cycle power plants

Abstract: All major manufacturers of large size gas turbines are developing new techniques aimed at achieving net electric efficiency higher than 60% in combined cycle applications. An essential factor for this goal is the effective cooling of the hottest rows of the gas turbine. The present work investigates three different approaches to this problem: (i) the most conventional open-loop air cooling; (ii) the closed-loop steam cooling for vanes and rotor blades; (iii) the use of two independent closed-loop circuits: steam for stator vanes and air for rotor blades. Reference is made uniquely to large size, single shaft units and performance is estimated through an updated release of the thermodynamic code GS, developed at the Energy Department of Politecnico di Milano. A detailed presentation of the calculation method is given in the paper. Although many aspects (such as reliability, capital cost, environmental issues) which can affect gas turbine design were neglected, thermodynamic analysis showed that efficiency higher than 61% can be achieved in the frame of current, available technology.

System for processing a workpiece

Abstract: A system for processing a workpiece includes a process head assembly and a base assembly. The process head assembly has a process head and an upper rotor. The base assembly has a base and a lower rotor. The base and lower rotor have magnets wherein the upper rotor is engageable with the lower rotor via a magnetic force created by the magnets. The engaged upper and lower rotors form a process chamber where a semiconductor wafer is positioned for processing. Process fluids for treating the workpiece are introduced into the process chamber, optionally while the processing head spins the workpiece. Additionally, air flow around and through the process chamber is managed to reduce particle adders on the workpiece.

Carrier signal injection based sensorless control methods for IPM synchronous machine drives

Abstract: This paper presents a comparison of carrier signal injection methods for sensorless torque and motion control of interior permanent magnet synchronous machine (IPMSM) drives. Rotor position can be identified at standstill and higher speeds by using one of two spatial saliency based high frequency carrier signal injection methods: rotating vector in the stationary frame or pulsating vector in the estimated rotor frame. Carrier currents for both rotating and pulsating voltage carrier injection are derived by using an IPMSM model for high frequency. An appropriate carrier signal extraction and a spatial saliency tracking scheme for both injection methods are developed for robust sensorless control. By interfering with the spatial saliency, saturation-induced saliencies act as disturbances to the rotor position estimation. Modeling, measurement, and analysis of the undesirable saturation-induced saliencies are presented for both carrier signal injection methods.

A microturbine for electric power generation

Abstract: A single-stage axial microturbine has been developed with a rotor diameter of 10 mm. This turbine is a first step in the development of a microgenerator that produces electrical energy from fuel. The turbine is made of stainless steel using die-sinking electro-discharge machining. It has been tested to speeds up to 160,000 rpm and generates a maximum mechanical power of 28 W with an efficiency of 18%. When coupled to a small generator, it generates 16 W of electrical power, which corresponds to an efficiency for the total system of 10.5%.

Detection of mechanical imbalances of induction machines without spectral analysis of time-domain signals

Abstract: Mechanical rotor imbalances and rotor eccentricities are reflected in electric, electromagnetic, and mechanical quantities. Therefore, many surveillance schemes determine the Fourier spectrum of a single line current in order to monitor the motor condition. Mechanical imbalances give rise to two first-order current harmonics. Due to the interaction of the currents and voltages, both these current harmonics are also reflected by a single harmonic component in the frequency spectrum of the electric power. This single component is easier to assess than both the current harmonics. The technique proposed in this contribution evaluates this imbalance-specific modulation of the electric power. The proposed approach does not determine the Fourier spectrum of a time-domain signal, though. First, the imbalance specific oscillation of the electric power is extracted by a bandpass filter. Then, the averaged pattern of this component is determined by means of an angular data clustering technique. In that way, the oscillation of the electric power in the time domain becomes mapped into a discrete waveform in an angular domain. The amplitude of the fundamental harmonic of these discrete data serves as the imbalance indicator of the proposed scheme. This technique, therefore, overcomes small load and slip fluctuations. Measured results of a mechanically unbalanced machine and a case of combined static and dynamic eccentricity are presented.

Sensorless aquisition of the rotor position angle for induction motors with arbitrary stator windings

Abstract: The anisotropy of a cage rotor is utilized to determine the angular position of the rotor in an induction machine. The switching transients generated by a pulsewidth controlled inverter serve as test signals. The response of the three inverter terminal currents is exploited to derive a quasi-instantaneous rotor position signal. The position is sensed at the inverter through the 3-phase motor cable by measuring the current derivatives. The method does not require additional wire connections. It is applicable to induction motors having the stator windings connected either in wye or in delta. The results are supported by measurements from an experimental setup.