Showing papers on "Rotor (electric) published in 2007"

Dynamic Modeling and Control of DFIG-Based Wind Turbines Under Unbalanced Network Conditions

Abstract: This paper presents an analysis and control design of a doubly-fed induction generator (DFIG)-based wind generation system operating under unbalanced network conditions. A DFIG system model in the positive and negative synchronous reference frames is presented. Variations of stator active and reactive powers and generator torque are fully defined in the presence of negative sequence voltage and current. Alternative DFIG control targets during network unbalance, such as reducing stator current unbalance, torque, and power pulsations minimization, are identified. A rotor current control strategy based on positive and negative (dq) reference frames is used to provide precise control of the rotor positive and negative sequence currents. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system. It shows that conventional vector control of DFIG without considering network unbalance results in excessive oscillations on the stator active/reactive power, electromagnetic torque, and stator/rotor currents even with a small stator voltage unbalance. In contrast, with the proposed control strategy, enhanced system control and operation such as minimizing oscillations in either active power, or electromagnetic torque, or stator or rotor currents can be achieved

Frequency support from doubly fed induction generator wind turbines

Abstract: An assessment on the capability of a doubly fed induction generator (DFIG) wind turbine for frequency regulation is presented. Detailed aerodynamic, structural and electrical dynamic models were used in this study. A control loop acting on the frequency deviation was added to the inertia contributing loop in order to enhance the inertia support from the DFIG wind turbine. The possibility of de-loading a wind turbine to provide primary and secondary frequency response was discussed. A frequency droop controller was examined where the droop is operating on the electronic torque set point below its maximum speed and is operating on the pitch demand at maximum speed. It is also shown that by reducing the generator torque set point the DFIG wind turbine can provide high frequency response.

Short-Circuit Current of Wind Turbines With Doubly Fed Induction Generator

Abstract: The short-circuit current contribution of wind turbines has not received much attention so far. This paper considers the short-circuit behavior, especially the short-circuit current of wind turbines with a doubly fed induction generator. Mostly, these wind turbines have a crowbar to protect the power electronic converter that is connected to the rotor windings of the induction generator. First, the maximum value of the short-circuit current of a conventional induction machine is determined. The differences between a crowbar-protected doubly fed induction generator and a conventional induction generator are highlighted and approximate equations for the maximum short-circuit current of a doubly fed induction generator are determined. The values obtained in this way are compared to the values obtained from time domain simulations. The differences are less then 15%

Motor having controllable torque

Abstract: A controllable motor includes a rotor. A first stator winding set is operable, upon being energized, to generate and apply a first torque to the rotor. A second stator winding set independent of the first stator winding set is operable, upon being energized, to generate and apply a second torque to the rotor. A motor control is coupled to the first and second stator winding sets. The motor control is operable to selectively energize one of the first or second stator winding sets to thereby generate and apply one of the first or second torques to the rotor, and simultaneously energize both the first and second stator winding sets to thereby generate and apply a third torque greater than the first or the second torque.

Surgical machine and method for controlling and/or regulating a surgical machine

Abstract: To improve a surgical machine with a sensorless electric motor comprising a rotor and at least two motor windings, and with a motor controller for controlling and/or regulating the electric motor, so that the electric motor is operable with optimum efficiency at low rotational speeds and a starting of the motor in accordance with the purpose, also under load, is enabled, it is proposed that a space vector pulse width modulation (SVPWM) method for controlling and/or regulating the electric motor, in which all motor windings are able to be simultaneously supplied with electric current, be performable with the motor controller. A method for controlling and/or regulating a surgical machine is also proposed.

Direct Power Control of DFIG With Constant Switching Frequency and Improved Transient Performance

Abstract: This paper proposes a new direct power control (DPC) strategy for a doubly fed induction generator (DFIG)-based wind turbine system. The required rotor control voltage, which eliminates active and reactive power errors within each fixed time period, is directly calculated based on stator flux, rotor position, and active and reactive powers and their corresponding errors. No extra power or current control loops are required, simplifying the system design, and improving transient performance. Constant converter switching frequency is achieved that eases the design of the power converter and the ac harmonic filter. Rotor voltage limit during transients is investigated, and a scheme is proposed that prioritizes the active and reactive power control such that one remains fully controlled while the error of the other is reduced. The impact of machine parameter variations on system performance is investigated and found negligible. Simulation results for a 2 MW DFIG system demonstrate the effectiveness and robustness of the proposed control strategy during variations of active and reactive power, machine parameters, and wind speed

Design of a Magnetic-Geared Outer-Rotor Permanent-Magnet Brushless Motor for Electric Vehicles

Abstract: This paper proposes a novel in-wheel motor, which artfully integrates a magnetic gear into a permanent-magnet brushless (PMBL) DC motor so that they can share a common PM rotor, hence offering both high efficiency and high power density. Moreover, the low-speed requirement for direct driving and the high-speed requirement for compact motor design can be achieved simultaneously. A 2-kW 600/4400-rpm magnetic-geared outer-rotor PMBL DC motor is designed and analyzed, which is particularly suitable for battery-powered electric motorcycles

Prophy angle and adapter

Abstract: A dental prophy angle includes a housing and a rotor. The housing defines a first bore and a second bore in communication with the first bore, and rotor is disposed within the second bore. The rotor includes a gearing system, and rotor includes a lock having a lock channel configured to receive a tip of a drive shaft. The housing includes a lock receiver for receiving the lock receiver permits rotation of the lock within the lock receiver and restrains linear movement of the lock in a direction substantially parallel to a rotational axis of the rotor.

Control of a Doubly Fed Induction Wind Generator Under Unbalanced Grid Voltage Conditions

Abstract: Wind energy is often installed in rural, remote areas characterized by weak, unbalanced power transmission grids. In induction wind generators, unbalanced three-phase stator voltages cause a number of problems, such as overcurrent, unbalanced currents, reactive power pulsations, and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance, induction wind generators are switched out of the network. This can further weaken the grid. In doubly fed induction generators (DFIGs), control of the rotor currents allows for adjustable speed operation and reactive power control. This paper presents a DFIG control strategy that enhances the standard speed and reactive power control with controllers that can compensate for the problems caused by an unbalanced grid by balancing the stator currents and eliminating torque and reactive power pulsations

A Magnetic-Geared Outer-Rotor Permanent-Magnet Brushless Machine for Wind Power Generation

Abstract: This paper presents a new permanent-magnet (PM) brushless machine for wind power generation. This machine adopts an outer-rotor topology, aiming at capturing wind power directly. In order to achieve high power density, a high-speed PM brushless generator is artfully integrated with a coaxial magnetic gear. The design details, with emphasis on the special constraints of wind power generation, are elaborated. By using the time-stepping finite element method, the static characteristics as well as no-load and on-load operations are simulated. A prototype is also built for experimentation. Both simulation and experimental results are given to verify the validity of the proposed machine. Finally, a quantitative comparison is made to justify that the proposed machine is of smaller size, lighter weight, and lower cost than its counterparts.

A new structure of a switching flux synchronous polyphased machine with hybrid excitation

Abstract: The aim of this paper is to present the structure of a new flux switching synchronous machine with hybrid excitation. This machine uses the flux switching principle where all the active parts are located on the stator. The rotor is only a salient passive rotor and can be robust and made with a low cost technology. This new machine can be supplied with electricity by means of a traditional three phase voltage converter or can be associated with a diode rectifier. The hybrid excitation is an association of permanent magnets and a wound exciter.

Speed-Sensorless Estimation for Induction Motors Using Extended Kalman Filters

Abstract: In this paper, extended-Kalman-filter-based estimation algorithms that could be used in combination with the speed-sensorless field-oriented control and direct-torque control of induction motors (IMs) are developed and implemented experimentally. The algorithms are designed aiming minimum estimation error in both transient and steady state over a wide velocity range, including very low and persistent zero-speed operation. A major challenge at very low and zero speed is the lost coupling effect from the rotor to the stator, which makes the information on rotor variables unobservable on the stator side. As a solution to this problem, in this paper, the load torque and the rotor angular velocity are simultaneously estimated, with the velocity taken into consideration via the equation of motion and not as a constant parameter, which is commonly the case in most past studies. The estimation of load torque, on the other hand, is performed as a constant parameter to account for Coulomb and viscous friction at steady state to improve the estimation performance at very low and zero speed. The estimation algorithms developed based on the rotor and stator fluxes are experimentally tested under challenging variations and reversals of the velocity and load torque (step-type and varying linearly with velocity) over a wide velocity range and at zero speed. In all the scenarios, the current estimation error has remained within a very narrow error band, also yielding acceptable velocity estimation errors, which motivate the use of the developed estimation method in sensorless control of IMs over a wide velocity range and persistent zero-speed operation

Modeling of Wind Turbines Based on Doubly-Fed Induction Generators for Power System Stability Studies

Abstract: This paper deals with modeling of the doubly-fed induction generator (DFIG) and the corresponding converter for stability studies. To enable efficient computation, a reduced-order DFIG model is developed that restricts the calculation to the fundamental frequency component. However, the model enhancement introduced in this paper allows the consideration of the alternating components of the rotor current as well, which is necessary for triggering the crowbar operation. Suitable models are presented for the rotor and grid side converters as well as the dc-link, taking into account all four possible operating modes. The proposed model for speed and pitch angle control can be used when wind and rotor speed variations are significant. Simulation results are presented for model verification purposes and also for demonstrating the dynamic behavior of a large offshore wind farm connected through a long undersea cable to the high voltage grid.

Online Stator and Rotor Resistance Estimation Scheme Using Artificial Neural Networks for Vector Controlled Speed Sensorless Induction Motor Drive

Abstract: This paper presents a new method of online estimation for the stator and rotor resistances of the induction motor for speed sensorless indirect vector controlled drives, using artificial neural networks. The error between the rotor flux linkages based on a neural network model and a voltage model is back propagated to adjust the weights of the neural network model for the rotor resistance estimation. For the stator resistance estimation, the error between the measured stator current and the estimated stator current using neural network is back propagated to adjust the weights of the neural network. The rotor speed is synthesized from the induction motor state equations. The performance of the stator and rotor resistance estimators and torque and flux responses of the drive, together with these estimators, are investigated with the help of simulations for variations in the stator and rotor resistances from their nominal values. Both resistances are estimated experimentally, using the proposed neural network in a vector controlled induction motor drive. Data on tracking performances of these estimators are presented. With this speed sensorless approach, the rotor resistance estimation was made insensitive to the stator resistance variations both in simulation and experiment. The accuracy of the estimated speed achieved experimentally, without the speed sensor clearly demonstrates the reliable and high-performance operation of the drive

Sensorless Indirect-Rotor-Field-Orientation Speed Control of a Permanent-Magnet Synchronous Motor With Stator-Resistance Estimation

Abstract: Efficient and precise sensorless speed control of a permanent-magnet synchronous motor (PMSM) requires accurate knowledge of rotor flux, position, and speed. In the literature, many sensorless schemes have been presented, in which the accurate estimation of rotor flux magnitude, position, and speed is guaranteed by detecting the back electromotive force (EMF). However, these schemes show great sensitivity to stator resistance mismatch and system noise, particularly, during low-speed operation. In this paper, an indirect-rotor-field-oriented-control scheme for sensorless speed control of a PMSM is proposed. The rotor-flux position is estimated by direct integration of the estimated rotor speed to reduce the effect of the system noise. The stator resistance and the rotor-flux speed and magnitude are estimated adaptively using stable model reference adaptive system estimators. Simple stability analysis and design of the estimators are performed using linear-control theory applied to an error model of the PMSM in a synchronous rotating reference frame. The convergence of rotor position- and speed-estimation errors to zero is guaranteed. Experimental results show excellent performance

Apparatus and method for controlling hybrid motor

Abstract: The present invention relates to an apparatus and method for controlling a hybrid motor, and more particularly, to an apparatus and method for controlling a hybrid motor, which uses a permanent magnet instead of a field coil for a rotor, winds a coil round a stator in a multi-phase independent parallel manner, fixes a rectifying type encoder to the rotor and connects a sensor to a driving circuit to smoothly start and rotate the hybrid motor, simplifies the configuration of the hybrid motor and reduce the manufacturing cost of the hybrid motor. The apparatus for controlling a hybrid motor having a multi-phase independent parallel stator coil comprises: an encoder attached to a rotor of the hybrid motor and operated in cooperation with a sensor in order to sense the pole of the rotor; the sensor for outputting a sensor signal indicating the polo of the rotor, sensed by the encoder; a speed input unit for generating a speed instruction signal for driving the motor; a power switching circuit for generating signals for driving the motor; a drive module for receiving the speed instruction signal and the sensor signal and outputting the speed instruction signal synchronized with the sensor signal as a signal for driving the motor; a power supply for applying a DC voltage to the power switching circuit; and a logic power supply for converting the DC voltage received from the power supply into a logic voltage and applying the converted logic voltage to the drive module. When the motor has n phases, the motor includes n power switching circuits and n drive modules.

Detecting Rotor Faults in Low Power Permanent Magnet Synchronous Machines

Abstract: This paper investigates the experimental implementation and detection of rotor faults in permanent magnet synchronous machines. Methods are shown how to experimentally introduce static and dynamic eccentricities and broken magnet cases. A new magnet flux estimation that does not require the measurement of the rotor position or speed is developed. The detection of these and other rotor faults by measuring only the stator currents and voltages are shown experimentally. The paper concludes by contributing a description of a condition-monitoring scheme for detection rotor faults

Variation in bat and bird fatalities at wind energy facilities: assessing the effects of rotor size and tower height

Abstract: Wind energy is a rapidly growing sector of the alternative energy industry in North America, and larger, more productive turbines are being installed. However, there are concerns regarding bird and...

Comparison of PM Motor Structures and Sensorless Control Techniques for Zero-Speed Rotor Position Detection

Abstract: The rotor position of a synchronous permanent magnet (PM) motor can be detected by means of the injection of a high-frequency stator voltage superimposed to the fundamental component. Thanks to the rotor anisotropy, the corresponding high-frequency current is modulated and used to determine the rotor position. Two techniques are considered: the first one adopts a pulsating voltage vector in the estimated synchronous reference frame, while the second one adopts a rotating voltage vector. These techniques are effective at zero and at low motor speed. The accuracy of the rotor position detection depends strictly on the rotor saliency, that is, on the geometry of the PM rotor. In fact both saturation and d-and q-axis cross-coupling have a heavy influence on the correct rotor position detection. The aim of this paper is to compare the two sensorless control techniques, together with two rotor geometries, that is, IPM and inset rotor. In order to highlight the effectiveness of the sensorless technique, the tests are carried out at various operating conditions. It is found that the effectiveness of the sensorless rotor position detection strongly depends on the PM rotor geometry. Conversely, the choice of the sensorless control technique affects slightly the rotor position detection.

Pole-Shape Optimization of a Switched-Reluctance Motor for Torque Ripple Reduction

Abstract: Switched-reluctance motors produce acoustic noise and vibration caused by torque ripple. Applications of these motors where silent operation is desirable, such as in home appliances, has, thus, been limited. This paper describes a proposal for a new stator pole face having a nonuniform air-gap and a pole shoe attached to the lateral face of the rotor pole. These additions minimize the undesired torque ripple. The effects of each design parameter were investigated using a time-stepping finite-element method. The parameters were optimized by utilizing response surface method (RSM) combined with (1 + 1) evolution strategy. It has been shown, through numerical tests, that the optimized shape gives higher average torque and drastically reduced torque ripple

Wafer processing system with dual wafer robots capable of asynchronous motion

Abstract: A robot assembly for transferring substrates includes a central tube assembly oriented along a central axis, perpendicular to a substrate transfer plane, and having an inner surface that forms part of a first enclosure at a first pressure, and an outer surface that forms part of a second enclosure at a second, different pressure. The robot assembly further includes a transfer robot which itself includes multiple rotor assemblies, each configured to rotate parallel to the substrate transfer plane. The various rotor assemblies are organized in pairs, each pair having one rotor fitted with a telescoping support arm/end effector arrangement to support substrates thereon, and the other rotor fitted with inner and outer actuator arms that cooperate to effect radial movement of the corresponding end effector of the paired rotor assembly. Each rotor is controlled to effect the transfer of substrates within a wafer processing system asynchronously and at differing heights.

Polyphasic multi-coil generator

Abstract: A polyphasic multi-coil generator includes a driveshaft, at least first and second rotors rigidly mounted on the driveshaft so as to simultaneously synchronously rotate with rotation of the driveshaft, and at least one stator sandwiched between the first and second rotors. The stator has an aperture through which the driveshaft is rotatably journalled. A stator array on the stator has an equally circumferentially spaced-apart array of electrically conductive coils mounted to the stator in a first angular orientation about the driveshaft. The rotors and the stator lie in substantially parallel planes. The first and second rotors have, respectively, first and second rotor arrays.

Apparatus and methods for magnetic alteration of anatomical features

Abstract: Systems and methods are disclosed for manipulating an anatomical feature within the body of the patient. An implant such as an internal jackscrew is implanted at the anatomical and has first and second attachment points that secure to spaced-apart locations on the anatomical feature, an internal rotor coupled to the jackscrew, and is configured to drive motion of the jackscrew to manipulate the anatomical feature. The system further includes an external rotor that is magnetically coupled to the internal rotor such that rotation of the external rotor at an exterior location to the patient's body affects a corresponding internal rotation of the internal rotor to manipulate the anatomical feature.

Improved Rotor Position Estimation by Signal Injection in Brushless AC Motors, Accounting for Cross-Coupling Magnetic Saturation

Abstract: This paper presents an improved signal-injection-based sensorless-control method for permanent-magnet brushless AC (BLAC) motors, accounting for the influence of cross-coupling magnetic saturation between the d- and q -axes. The d- and q -axis incremental self-inductances, the incremental mutual inductance between the d-axis and q -axis, and the cross-coupling factor are determined by finite-element analysis. An experimental method is proposed for measuring the cross-coupling factor which can be used directly in the sensorless-control scheme. Both measurements and predictions show that a significant improvement in the accuracy of the rotor-position estimation can be achieved under both dynamic and steady-state operation compared with that which is obtained with the conventional signal-injection method.

Effect of Axial Segmentation of Permanent Magnets on Rotor Loss in Modular Permanent-Magnet Brushless Machines

Abstract: This paper presents a computationally efficient technique in determining the influence of the finite axial length of the permanent magnets on the rotor eddy-current loss in modular brushless ac machines. The technique is employed to quantify the effectiveness of axially segmenting the permanent magnets of four-phase, eight-slot, ten-pole and five-phase, ten-slot, 12-pole brushless machines, which have been designed to meet the performance requirements of an electromechanical flight control surface actuator for a "more-electric" aircraft.

Reactive power capability of a wind turbine with doubly fed induction generator

Abstract: The aim of the work is to derive a steady state PQ-diagram for a variable speed wind turbine equipped with a Doubly Fed Induction Generator. Firstly, the dependency between optimal rotor speed and wind speed is presented. Secondly, the limitations in reactive power production, caused by the rotor current, the rotor voltage and the stator current are derived. Thirdly, the influence of switching from Δ to Y coupling of the stator is investigated. Finally, a complete PQ diagram for a wind turbine is plotted. It is concluded that the limiting factor regarding reactive power production will typically be the rotor current limit, and that the limit for reactive power absorption will be the stator current limit. Further, it is concluded that the rotor voltage will only have a limiting effect at high positive and negative slips, but near the limitation, the reactive power capability is very sensitive to small changes in the slip. Copyright © 2007 John Wiley & Sons, Ltd.

Sliding-Mode Flux Observer With Online Rotor Parameter Estimation for Induction Motors

Abstract: Field orientation techniques without flux measurements depend on the parameters of the motor, particularly on the rotor resistance or rotor time constant (for rotor field orientation). Since these parameters change continuously as a function of temperature, it is important that the value of rotor resistance is continuously estimated online. A fourth-order sliding-mode flux observer is developed in this paper. Two sliding surfaces representing combinations of estimated flux and current errors are used to enforce the flux and current estimates to their real values. Switching functions are used to drive the sliding surfaces to zero. The equivalent values of the switching functions (low-frequency components) are proven to be the rotor resistance and the inverse of the rotor time constant. This property is used to simultaneously estimate the rotor resistance and the inverse of the time constant without prior knowledge of either the rotor resistance or the magnetizing inductance. Simulations and experimental results prove the validity of the proposed approach

Dynamic Eccentricity and Demagnetized Rotor Magnet Detection in Trapezoidal Flux (Brushless DC) Motors Operating Under Different Load Conditions

Abstract: Brushless dc (BLDC) machines are finding increasing use in applications that demand high and rugged performance. Automotive and aerospace are some such areas where these machines may be used. In this context, condition monitoring of these machines would provide added value. This paper investigates the effect of several potential rotor faults on the current spectrum of BLDC motors with a view to develop an effective condition-monitoring scheme. The effect of load unbalances, misalignments, and varying load torques on the diagnosis of such machines is investigated. A method to estimate the strength of the rotor magnets is also provided. Simulation and experimental results are presented to substantiate that current signature analysis could be a viable tool for diagnosing the condition of BLDC machines.