Showing papers on "Rotor (electric) published in 2008"

Models for Bearing Damage Detection in Induction Motors Using Stator Current Monitoring

Abstract: This paper describes a new analytical model 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 the following two effects of a bearing fault: 1. the introduction of a particular radial rotor movement and 2. 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.

Model Reference Adaptive Controller-Based Rotor Resistance and Speed Estimation Techniques for Vector Controlled Induction Motor Drive Utilizing Reactive Power

Abstract: In this paper, a detailed study on the model reference adaptive controller (MRAC) utilizing the reactive power is presented for the online estimation of rotor resistance to maintain proper flux orientation in an indirect vector controlled induction motor drive. Selection of reactive power as the functional candidate in the MRAC automatically makes the system immune to the variation of stator resistance. Moreover, the unique formation of the MRAC with the instantaneous and steady-state reactive power completely eliminates the requirement of any flux estimation in the process of computation. Thus, the method is less sensitive to integrator-related problems like drift and saturation (requiring no integration). This also makes the estimation at or near zero speed quite accurate. Adding flux estimators to the MRAC, a speed sensorless scheme is developed. Simulation and experimental results have been presented to confirm the effectiveness of the technique.

Analysis and Optimization of Back EMF Waveform of a Flux-Switching Permanent Magnet Motor

Abstract: Flux-switching permanent magnet (FSPM) motors have a doubly salient structure, the magnets being housed in the stator and the stator winding comprising concentrated coils. They have attracted considerable interest due to their essentially sinusoidal phase back electromotive force (EMF) waveform. However, to date, the inherent nature of this desirable feature has not been investigated in detail. Thus, a typical three-phase FSPM motor with 12 stator teeth and ten rotor poles is considered. It is found that, since there is a significant difference in the magnetic flux paths associated with the coils of each phase, this results in harmonics in the coil back EMF waveforms being cancelled, resulting in essentially sinusoidal phase back EMF waveforms. In addition, the influence of the rotor pole-arc on the phase back EMF waveform is evaluated by finite-element analysis, and an optimal pole-arc for minimum harmonic content in the back EMF is obtained and verified experimentally.

Active Flux Concept for Motion-Sensorless Unified AC Drives

Abstract: Rotor and stator flux orientations are now standard concepts in vector and direct torque control of ac drives. The salient-pole rotor machines, where magnetic saturation plays a key role, still pose notable problems in flux, rotor position and speed estimations for motion-sensorless control, especially in the low-speed range (below 30 rpm in general), leading to numerous dedicated state observers. This letter introduces a rather novel (or generalization) concept-active flux or torque-producing flux-and its utilization in all ac drives by employing a unified state observer for motion-sensorless control in a wide speed range. The active-flux concept turns all salient-pole traveling field machines into nonsalient-pole ones. The active-flux vector is aligned to the rotor d axis for all synchronous machines and to the rotor-flux vector axis for induction machines. This way, the rotor position and speed observer seems more amenable to a wide speed range, with smaller dynamic errors. This observer, based on the active-flux concept, is pretty much the same for all ac drives. An example of implementation for an interior permanent-magnet synchronous motor with weak permanent magnets and large magnetic saliency that compares very favorably with respect to most signal injection methods, down to 1 rpm and up to 4000 rpm, is provided through digital simulations. Experiments are under way.

Coordinated Control of DFIG's Rotor and Grid Side Converters During Network Unbalance

Abstract: This paper proposes a coordinated control of the rotor side converters (RSCs) and grid side converters (GSCs) of doubly-fed induction generator (DFIG) based wind generation systems under unbalanced voltage conditions. System behaviors and operations of the RSC and GSC under unbalanced voltage are illustrated. To provide enhanced operation, the RSC is controlled to eliminate the torque oscillations at double supply frequency under unbalanced stator supply. The oscillation of the stator output active power is then cancelled by the active power output from the GSC, to ensure constant active power output from the overall DFIG generation system. To provide the required positive and negative sequence currents control for the RSC and GSC, a current control strategy containing a main controller and an auxiliary controller is analyzed. The main controller is implemented in the positive (dq)+ frame without involving positive/negative sequence decomposition whereas the auxiliary controller is implemented in the negative sequence (dq)- frame with negative sequence current extracted. Simulation results using EMTDC/PSCAD are presented for a 2 MW DFIG wind generation system to validate the proposed control scheme and to show the enhanced system operation during unbalanced voltage supply.

Induction Machine Broken Bar and Stator Short-Circuit Fault Diagnostics Based on Three-Phase Stator Current Envelopes

Abstract: A new method for the fault diagnosis of a broken rotor bar and interturn short circuits in induction machines (IMs) is presented. The method is based on the analysis of the three-phase stator current envelopes of IMs using reconstructed phase space transforms. The signatures of each type of fault are created from the three-phase current envelope of each fault. The resulting fault signatures for the new so-called ldquounseen signalsrdquo are classified using Gaussian mixture models and a Bayesian maximum likelihood classifier. The presented method yields a high degree of accuracy in fault identification as evidenced by the given experimental results, which validate this method.

Sliding Mesh Algorithm for CFD Analysis of Helicopter Rotor-Fuselage Aerodynamics

Abstract: SUMMARY The study of rotor–fuselage interactional aerodynamics is central to the design and performance analysis of helicopters. However, regardless of its significance, rotor–fuselage aerodynamics has so far been addressed by very few authors. This is mainly due to the difficulties associated with both experimental and computational techniques when such complex configurations, rich in flow physics, are considered. In view of the above, the objective of this study is to develop computational tools suitable for rotor–fuselage engineering analysis based on computational fluid dynamics (CFD). To account for the relative motion between the fuselage and the rotor blades, the concept of sliding meshes is introduced. A sliding surface forms a boundary between a CFD mesh around the fuselage and a rotor-fixed CFD mesh which rotates to account for the movement of the rotor. The sliding surface allows communication between meshes. Meshes adjacent to the sliding surface do not necessarily have matching nodes or even the same number of cell faces. This poses a problem of interpolation, which should not introduce numerical artefacts in the solution and should have minimal effects on the overall solution quality. As an additional objective, the employed sliding mesh algorithms should have small CPU overhead. The sliding mesh methods developed for this work are demonstrated for both simple and complex cases with emphasis placed on the presentation of the inner workings of the developed algorithms. Copyright q 2008 John Wiley & Sons, Ltd.

Sensorless Control of Doubly-Fed Induction Generators Using a Rotor-Current-Based MRAS Observer

Abstract: This paper presents a new sensorless method for the vector control of doubly-fed induction machines (DFIMs) without using speed sensors or rotor position measurements. The proposed sensorless method is based on the model reference adaptive system (MRAS) estimating the rotor position and speed from the machine rotor currents. The method is appropriate for both stand-alone and grid-connected operation of variable speed DFIMs. To design the MRAS observer with the appropriate dynamic response, a small signal model is derived. The sensitivity of the method for variation in the machine parameters is also analyzed. Speed catching on the fly and synchronization of the doubly-fed induction generator with the utility are also addressed. Experimental results obtained from a 3.5-kW prototype are presented and fully analyzed.

Sensorless Control of Doubly-Fed Induction Generators Using a Rotor-Current-Based

Abstract: This paper presents a new sensorless method for the vector control of Doubly-Fed Induction Machines (DFIMs) without using speed sensors or rotor position measurements. The proposed sensorless method is based on the Model Reference Adaptive System (MRAS) estimating the rotor position and speed from the machine rotor currents. The method is appropriate for both stand-alone and grid-connected operation of variable speed DFIMs. To design the MRAS observer with the appropriate dy- namic response, a small signal model is derived. The sensitivity of the method for variation in the machine parameters is also analyzed. Speed catching on the fly and synchronization of the Doubly-Fed Induction Generator with the utility are also ad- dressed. Experimental results obtained from a 3.5-kW prototype are presented and fully analyzed.

Combined Flux Observer With Signal Injection Enhancement for Wide Speed Range Sensorless Direct Torque Control of IPMSM Drives

Abstract: This paper proposes a motion-sensorless control system using direct torque control with space vector modulation for interior permanent magnet synchronous motor (IPMSM) drives, for wide speed range operation, including standstill. A novel stator flux observer with variable structure uses a combined voltage-current model with PI compensator for low-speed operations. As speed increases, the observer switches gradually to a PI compensated closed-loop voltage model, which is solely used at high speeds. High-frequency rotating-voltage injection with a single D-module bandpass vector filter and a phase-locked loop state observer with a new synchronization procedure are used to estimate the rotor position, which is needed only by the current model in stator flux observer at low speeds. A new rotor speed estimator for the whole speed-loop range, based on the stator flux speed estimation with a new dynamic correction depending on estimated torque, is proposed and tested. Extensive simulation results and significant experimental results provided good performance for the proposed IPMSM sensorless system in more than 1:1000 speed range, under full-load operation, from very low speeds (1 r/min experimental) up to rated speed.

Two-Level VSC Based Predictive Direct Torque Control of the Doubly Fed Induction Machine With Reduced Torque and Flux Ripples at Low Constant Switching Frequency

Abstract: In this paper, a new predictive direct torque control (DTC) strategy of the doubly fed induction machine (DFIM) is presented. It is especially designed to operate at a considerably low constant switching frequency, reducing the electromagnetic torque and rotor flux ripples, in order to provide good steady-state and fast dynamic performances. This control is convenient for high power drive and generator applications, with restricted switching frequency. The DFIM is connected to the grid by the stator and the rotor is fed by a two level voltage source converter. In addition, this control method allows to implement a technique that reduces the switching power losses of the converter. Finally, experimental results show that the proposed DTC method effectively reduces the torque and flux ripples at low switching frequency, even under variable speed operation conditions.

Modelling and control of variable-speed multi-pole permanent magnet synchronous generator wind turbine

Abstract: Emphasis of this article is on variable-speed pitch-controlled wind turbines with multi-pole permanent magnet synchronous generator (PMSG) and on their extremely soft drive-train shafts. A model and a control strategy for a full back-to-back converter wind turbine with multi-pole PMSG are described. The model comprises submodels of the aerodynamic rotor, the drive-train by a two-mass model, the permanent magnet generator and the full-scale converter system. The control strategy, which embraces both the wind turbine control itself and the control of the full-scale converter, has tasks to control independently the active and reactive powers, to assist the power system and to ensure a stable normal operation of the wind turbine itself. A multi-pole PMSG connected to the grid through a full-scale converter has no inherent damping, and therefore, such configuration can become practically unstable, if no damping by means of external measures is applied. In this work, the frequency converter is designed to damp actively the drive-train oscillations, thus ensuring stable operation. The dynamic performance of the presented model and control strategy is assessed and emphasized in normal operation conditions by means of simulations in the power system simulation tool DIgSILENT. Copyright © 2008 John Wiley & Sons, Ltd.

Rotary electric machine

Abstract: PROBLEM TO BE SOLVED: To provide a rotary electric machine wherein even in a stator provided with a concentrated winding, a rotor can be directly positioned in the position of magnetization by passing a direct current through the winding of the stator SOLUTION: The rotary electric machine includes the rotor 10 and the stator 1 The rotor 10 has the following on the outer circumference of a rotating shaft 11: a core inner radius portion 12; magnet insertion holes 13 into which permanent magnets are inserted; a core outer radius portion 14; and connecting portions 15 placed between adjoining magnet insertion holes 13 and magnetically connecting the core inner radius portion 13 and the core outer radius portion 14 The stator 1 is disposed outside the rotor 10 and includes multiple salient poles 2 and concentrated windings of multiple phases wound on the salient poles 2 The connecting portions 15 of the rotor 10 are provided on the outer radius side with: thick portions 20 whose thickness in the radial direction is increased over a circumferential range equal to or wider than the gap 4 between the tips of adjoining salient poles 2 of the stator 1; and thin portions 21 whose thickness in the radial direction is small, positioned on both sides of the thick portions 20 in the circumferential direction COPYRIGHT: (C)2008,JPO&INPIT

Direct Power Control Applied to Doubly Fed Induction Generator Under Unbalanced Grid Voltage Conditions

Abstract: This paper analyzes the effects of unbalanced voltage on doubly fed induction generators. It also presents a novel control strategy based on direct power control (DPC+) applied to this type of generators, predominant in wind energy applications, that enables them to work under perturbed conditions and achieve optimum results. Although the technique can be implemented to control both rotor converters and grid converters, we will hereby exemplify the former which regulates stator active and reactive power. The results obtained with DPC+ are then compared through experimental tests to indicate that the technique is suitable and achieves good dynamic responses while controlling current distortion, power or torque oscillations. The validation of results has been performed through experimental tests on a 20-kW generator.

Wound Rotor Induction Generator With Sensorless Control and Integrated Active Filter for Feeding Nonlinear Loads in a Stand-Alone Grid

Abstract: This paper describes a vector control scheme for a stand-alone generator based on a wound rotor induction machine with rotor side control. The stand-alone generator refers to an isolated grid feeding a local load. The primary objective of the control scheme is to maintain constant voltage and frequency at the output of the generator irrespective of prime mover speed variation. A novel, simple, and easily implementable sensorless control scheme is proposed. The issue of power quality, which is one of the main concerns of a stand-alone generation system, is also addressed. This is done by incorporating the active filter concept in the control scheme to cancel significant harmonics. A method of unit vector generation for field-oriented control is proposed. A laboratory prototype consisting of back-to-back insulated-gate bipolar transistor converters and a TMS320F240 DSP controller is developed. Detailed experimental results are presented which demonstrate and validate the effectiveness of the proposed scheme.

DFIG-Based Power Generation System With UPS Function for Variable-Speed Applications

Abstract: The power generation system with a doubly fed induction generator (DFIG), which can be used as an autonomous power system after the loss of mains in a distributed generation network, is described. After the mains outage, a fixed frequency and an amplitude of the output voltage are obtained, despite the variable rotor speed. For this reason, it can be successfully applied in the variable-speed wind turbines, adjustable speed water plants, or diesel engines. Moreover, the stand-alone operation of DFIG is useful in a flywheel-based high-energy rotary uninterruptible power supply system. An output voltage is controlled directly by the synchronization of an actual voltage vector with the reference vector represented in a synchronously rotating polar frame. The rotor current angular speed is obtained as a result of vectorial phase-locked loop operation. Any sensors or estimators of the rotor speed or position are unnecessary. Both amplitude and angle control loops are linear. The use of stand-alone operation in grid-connected systems requires mains outage detection. Also, the grid voltage recovery requires a method of synchronization and soft connection of a generator to the grid. The proposed methods of output voltage control, synchronization, and detection of mains loss were tested in a laboratory system.

Chip-Firing and Rotor-Routing on Directed Graphs

Abstract: We give a rigorous and self-contained survey of the abelian sandpile model and rotor-router model on finite directed graphs, highlighting the connections between them. We present several intriguing open problems.

Experimental Evaluation of Braided EKF for Sensorless Control of Induction Motors

Abstract: Temperature- and frequency-dependent variations of the rotor (R'r) and stator (Rs) resistances pose a challenge in the accurate estimation of flux and velocity in the sensorless control of induction motors (IMs) over a wide speed range. Solutions have been sought to the problem by signal injection and/or by the use of different algorithms for the different parameters and states of the same motor. In this paper, a novel Extended-Kalman-Filter (EKF)-based estimation technique is developed for the solution of the problem based on the consecutive operation of two EKF algorithms at every time step. The proposed ldquobraidedrdquo EKF technique is experimentally tested under challenging parameter and load variations in a wide speed range, including low speed. The results demonstrate a significantly increased accuracy in the estimation of Rs and R'r, as well as load torque, flux, and velocity in transient and steady state, when compared with single EKFs or other approaches taken to estimate these parameters and states in the sensorless control of IMs. The improved results also motivate the utilization of the new estimation approach in combination with a variety of control methods which depend on accurate knowledge of a high number of parameters and states.

On the proof of concept of a ‘Smart’ wind turbine rotor blade for load alleviation

Abstract: The trend with offshore wind turbines is to increase the rotor diameter as much as possible to decrease the costs per kilowatt-hour. The increasing dimensions have led to the relative increase of the loads on the wind turbine structure. Because of the increasing rotor size and the spatial load variations along the blade, it is necessary to react to turbulence in a more detailed way; each blade separately and at several separate radial distances. In this paper, a proof of concept study is performed to show the feasibility of the load alleviation abilities of a ‘Smart’ blade, i.e. a blade equipped with a number of control devices that locally change the lift profile on the blade, combined with appropriate sensors and feedback controllers. Theoretical and experimental models are developed of a scaled non-rotating rotor blade which is equipped with two trailing edge flaps and strain sensors to facilitate feedback control. A pitch actuator is used to induce disturbances with a similar character as a gust or turbulence. A feedback controller based on classical loop shaping is designed that minimizes the root bending moment in the flapping direction. We show that with appropriate control techniques, the loads for periodic disturbances and for turbulence generated disturbances can be reduced up to 90 and 55%, respectively. Copyright © 2008 John Wiley & Sons, Ltd.

Systems and methods for powering a gimbal mounted device

Abstract: Gimbal power systems and methods are operable to provide power to a device attached to the gimbal. An exemplary embodiment is configured to rotate a rotational member of the gimbal system about an axis, wherein a stator of a rotary power transformer affixed to the rotational member rotates about the axis, and wherein an end of an electrical connection coupled to a power connector of a rotor winding of the rotary power transformer remains substantially stationary as the stator of the rotary power transformer rotates about the axis.

High Frequency Resolution Techniques for Rotor Fault Detection of Induction Machines

Abstract: Motor current signature analysis (MCSA) is the reference method for the diagnosis of medium-large machines in industrial applications. However, MCSA is still an open research topic, as some signatures may be created by different phenomena, wherein it may become sensitive to load and inertia variations, and with respect to an oscillating load torque, although suitable data normalization can be applied. Recently, the topic of diagnostic techniques for drives and low to medium size machines is becoming attractive, as the procedure can be embedded in the drive at no additional thanks to a dedicated firmware, provided that a suitable computational cost is available. In this paper, statistical time-domain techniques are used to track grid frequency and machine slip. In this way, either a lower computational cost or a higher accuracy than traditional discrete Fourier transform techniques can be obtained. Then, the knowledge of both grid frequency and machine slip is used to tune the parameters of the zoom fast Fourier transform algorithm that either increases the frequency resolution, keeping constant the computational cost, or reduces the computational cost, keeping constant the frequency resolution. The proposed technique is validated for rotor faults.

Finite-Element Transient Analysis of Induction Motors Under Mixed Eccentricity Fault

Abstract: In a three-phase squirrel-cage induction motor, eccentricity is a common fault that can make it necessary to remove the motor from the production line. However, because the motor may be inaccessible, diagnosing the fault is not easy. We have developed a time-stepping finite-element method (FEM) that identifies mixed eccentricity (a combination of static and dynamic) by analysis, without direct access to the motor. The method overcomes the difficulty of applying FEMs to transient behavior. It simulates the spectrum of the line current of a production-line motor and compares it to the spectrum of a known healthy motor to detect eccentricity. Agreement between the simulation and actual measurements of eccentricity is good.Protection and fault diagnosis are integral to sound application of three-phase squirrel-cage induction motors in industry. Eccentricity is a common fault in induction motors that might force the motor to be removed from the production line. However, diagnosis of this fault due to inaccessibility to the rotor is not easy. Performance analysis, investigation and diagnosis of static, dynamic and mixed eccentricities at steady-state and during transient modes have already been published using analytical methods. However, study of static and dynamic eccentricities only at steady-state using finite element method (FEM) has been previously reported. This paper uses time stepping FE (TSFE) method with voltage-fed source for performance analysis and diagnosis of mixed eccentricity in induction motor at start up. The method used here overcomes the difficulty of FE application which makes it possible to analyze the transient behavior of a faulty induction motor. Spectra of line current of healthy motor and motor under mixed eccentricity conditions are predicted by simulation and then compared with the experimental results. This comparison shows a very good agreement between the simulation and test results.

Multi-Phase Flux-Switching Permanent Magnet Brushless Machine for Aerospace Application

Abstract: Flux-switching permanent-magnet (FSPM) brushless machines have attracted considerable interest as a candidate machine technology for applications requiring high torque density and robust rotors. To date, published findings have focused exclusively on single and three phase FSPM machines. This paper investigates FSPM brushless machines of higher phase numbers, by means a detailed comparison of the electromagnetic performance of 3-, 4-, 5-, 6-phase variants within the specific context of aerospace generators. Machines having both all poles and alternate poles wound are investigated, the latter offering scope to reduce mutual coupling between phases so as to achieve improved fault-tolerance. The finite element predicted back-EMF waveforms are experimentally validated on small 5-phase FSPM machines having all poles wound and alternate poles wound. The nature of the generator specification requires that consideration must be given to mechanical stress in the rotor and the trade-off with electromagnetic design considerations, notably the degree of rotor saliency which can be incorporated. Therefore, a mechanical finite element study of the rotor mechanical stresses of multi-phase FSPM machines is also comparatively assessed.

Whirl and whip instabilities in rotor-bearing system considering a nonlinear force model

Abstract: Linear models and synchronous response are generally adequate to describe and analyze rotors supported by hydrodynamic bearings. Hence, stiffness and damping coefficients can provide a good model for a wide range of situations. However, in some cases, this approach does not suffice to describe the dynamic behavior of the rotor-bearing system. Moreover, unstable motion occurs due to precessional orbits in the rotor-bearing system. This instability is called “oil whirl” or “oil whip”. The oil whirl phenomenon occurs when the journal bearings are lightly loaded and the shaft is whirling at a frequency close to one-half of rotor angular speed. When the angular speed of the rotor reaches approximately twice the natural frequency (first critical speed), the oil whip phenomenon occurs and remains even if the rotor angular speed increases. Its frequency and vibration mode correspond to the first critical speed. The main purpose of this paper is to validate a complete nonlinear solution to simulate the fluid-induced instability during run-up and run-down. A flexible rotor with a central disk under unbalanced excitation is modeled. A nonlinear hydrodynamic model is considered for short bearing and laminar flow. The effects of unbalance, journal-bearing parameters and rotor arrangement (vertical or horizontal) on the instability threshold are verified. The model simulations are compared with measurements at a real vertical power plant and a horizontal test rig.

Doubly Fed Induction Machines Diagnosis Based on Signature Analysis of Rotor Modulating Signals

Abstract: This paper introduces an advanced monitoring and diagnosis system for the detection of incipient electrical faults in doubly fed induction generators used in wind turbines. In this application, the rotor is supplied by a static converter for the control of active and reactive power flows from the generator to the electrical grid. A new diagnostic method based on the frequency analysis of the rotor modulating signals is proposed. Simulation and experimental results confirm that a convenient frequency analysis of these signals and a simple interpretation lead to an effective diagnostic procedure. The proposed system is suitable to be easily embedded in the power-converter digital control system at very low cost.

Low Order PWM Inverter Harmonics Contributions to the Inverter-Fed Induction Machine Fault Diagnosis

Abstract: In this paper, the effects of inverter harmonics on motor current fault signatures are studied in detail. It is theoretically and experimentally shown that the fault signatures caused by the inverter harmonics are similar and comparable to those generated by the fundamental harmonic on the line current. Theoretically-derived extended relations including bearing fault, eccentricity, and broken rotor bar relations are found to match experimental results. Furthermore, it is observed and reported that the asymmetries on the rotor caused by broken rotor bars increase the amplitude of even harmonics. To confirm these claims, bearing, eccentricity, and broken rotor bar faults are tested and the line current spectrum of each faulty motor is compared with the healthy one. The proposed additional fault data are expected to contribute positively to the inverter-fed motor fault decision making algorithms.