Showing papers on "Rotor (electric) published in 1996"

Doubly fed induction generator using back-to-back PWM converters and its application to variable-speed wind-energy generation

Abstract: The paper describes the engineering and design of a doubly fed induction generator (DFIG), using back-to-back PWM voltage-source converters in the rotor circuit. A vector-control scheme for the supply-side PWM converter results in independent control of active and reactive power drawn the supply, while ensuring sinusoidal supply currents. Vector control of the rotor-connected converter provides for wide speed-range operation; the vector scheme is embedded in control loops which enable optimal speed tracking for maximum energy capture from the wind. An experimental rig, which represents a 7.5 kW variable speed wind-energy generation system is described, and experimental results are given that illustrate the excellent performance characteristics of the system. The paper considers a grid-connected system; a further paper will describe a stand-alone system.

A doubly fed induction generator using back-to-back PWM converters supplying an isolated load from a variable speed wind turbine

Abstract: A doubly fed induction generator (DFIG) designed to be driven at variable speed from a wind turbine and supplying an isolated load is presented. Two back-to-back PWM voltage-fed inverters connected between the stator and the rotor allow sub- and super-synchronous operation with low distortion currents. The load voltage is maintained at constant frequency and its magnitude is regulated through control of the stator flux of the generator. An auxiliary load is connected in parallel with the main load, and the auxiliary power is controlled to allow the DFIG to track the optimal wind turbine speed for maximum energy capture from the wind. An indirect stator-orientated vector control scheme is used to control the DFIG and this results in constant load voltage and frequency for variations in both load and wind speed. The techniques have been implemented and validated on a 7.5 kW experimental rig.

AI techniques in induction machines diagnosis including the speed ripple effect

Abstract: Various applications of artificial intelligence (AI) techniques (expert systems, neural networks, and fuzzy logic) presented in the literature prove that such technologies are well suited to cope with on-line diagnostic tasks for induction machines. The features of these techniques and the improvements that they introduce in the diagnostic process are recalled, showing that, in order to obtain an indication on the fault extent, faulty machine models are still essential. Moreover, by the models, that must trade off between simulation result effectiveness and simplicity, it is possible to overcome crucial points of the diagnosis. With reference to rotor electrical faults of induction machines, a new and simple procedure based on a model which includes the speed ripple effect is developed. This procedure leads to a new diagnostic index, independent of the machine operating condition and inertia value, that allows the implementation of the diagnostic system with a minimum configuration intelligence.

Sensorless PM brushless DC motor drives

Abstract: To control PM brushless DC motors, position and speed sensors are indispensable because the current should be controlled depending on the rotor position. However, these sensors are undesirable from standpoints of size, cost, maintenance, and reliability. There are different ways of approaching this problem, depending on the flux distribution. The paper presents the speed and position sensorless control of PM brushless DC motors with a sinusoidal flux distribution. Two approaches are presented and compared with each other; one is based on the voltage model of the motor and another is based on the current model. The starting procedure is also a very difficult problem under sensorless drives, because the sensorless drive algorithm uses voltage and current for estimation of rotor position, but no information is available before starting. A novel starting method is presented by using a salient-pole machine. Experimental results based on DSP-TMS320C25 controller are shown for comparisons, which demonstrate desired characteristics both in steady-state and starting conditions.

Source of induction motor bearing currents caused by PWM inverters

Abstract: The recent increase of bearing damage in induction machines driven by transistorized inverters has spurred activity on possible causes related to PWM inverters. This paper looks into a typical power conversion system from this perspective. It identifies the existence of the common mode voltages produced in all types of converters. A hypothesis is then proposed to explain the bearing current problem. In particular, it is shown that in an inverter-motor system the common mode voltages generated by a PWM inverter, which are attributed to PWM switching harmonics, couple through parasitic capacitances from stator windings to the rotor body and then returns through the motor bearings to the commonly grounded stator case as a closed loop circuit. The hypothesis is verified by experimental measurement of common mode coupling currents and true bearing currents in a specially modified induction motor. Solutions are then provided to suppress the bearing currents.

Identification and compensation of torque ripple in high-precision permanent magnet motor drives

Abstract: Permanent magnet synchronous machines generate parasitic torque pulsations owing to distortion of the stator flux linkage distribution, variable magnetic reluctance at the stator slots, and secondary phenomena. The consequences are speed oscillations which, although small in magnitude, deteriorate the performance of the drive in demanding applications. The parasitic effects are analyzed and modeled using the complex state-variable approach. A fast current control system is employed to produce high-frequency electromagnetic torque components for compensation. A self-commissioning scheme is described which identifies the machine parameters, particularly the torque ripple functions which depend on the angular position of the rotor. Variations of permanent magnet flux density with temperature are compensated by on-line adaptation. The algorithms for adaptation and control are implemented in a standard microcontroller system without additional hardware. The effectiveness of the adaptive torque ripple compensation is demonstrated by experiments.

Chaotic motions of a rigid rotor in short journal bearings

Abstract: In the present paper the conditions that give rise to chaotic motions in a rigid rotor on short journal bearings are investigated and determined. A suitable symmetry was given to the rotor, to the supporting system, to the acting system of forces and to the system of initial conditions, in order to restrict the motions of the rotor to translatory whirl. For an assigned distance between the supports, the ratio between the transverse and the polar mass moments of the rotor was selected conveniently small, with the aim of avoiding conical instability. Since the theoretical analysis of a system's chaotic motions can only be carried out by means of numerical investigation, the procedure here adopted by the authors consists of numerical integration of the rotor's equations of motion, with trial and error regarding the three parameters that characterise the theoretical model of the system: m, the half non-dimensional mass of the rotor, σ, the modified Sommerfeld number relating to the lubricated bearings, and ρ, the dimensionless value of rotor unbalance. In the rotor's equations of motion, the forces due to the lubricating film are written under the assumption of isothermal and laminar flow in short bearings. The number of numerical trials needed to find the system's chaotic responses has been greatly reduced by recognition of the fact that chaotic motions become possible when the value of the dimensionless static eccentricity % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbnL2yY9% 2CVzgDGmvyUnhitvMCPzgarmWu51MyVXgaruWqVvNCPvMCG4uz3bqe% fqvATv2CG4uz3bIuV1wyUbqee0evGueE0jxyaibaieYlf9irVeeu0d% Xdh9vqqj-hEeeu0xXdbba9frFf0-OqFfea0dXdd9vqaq-JfrVkFHe9% pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaaca% qabeaadaabauaaaOqaaiabew7aLnaaBaaaleaacaWGZbaabeaaaaa!4046!\[\varepsilon _s \] is greater than 0.4. In these conditions, non-periodic motions can be obtained even when rotor unbalance values are not particularly high (ρ=0.05), whereas higher values (ρ>0.4) make the rotor motion periodic and synchronous with the driving rotation. The present investigation has also identified the route that leads an assigned rotor to chaos when its angular speed is varied with prefixed values of the dimensionless unbalance ρ. The theoretical results obtained have then been compared with experimental data. Both the theoretical and the experimental data have pointed out that in the circumstances investigated chaotic motions deserve more attention, from a technical point of view, than is normally ascribed to behaviours of this sort. This is mainly because such behaviours are usually considered of scarce practical significance owing to the typically bounded nature of chaotic evolution. The present analysis has shown that when the rotor exhibits chaotic motions, the centres of the journals describe orbits that alternate between small and large in an unpredictable and disordered manner. In these conditions the thickness of the lubricating film can assume values that are extremely low and such as to compromise the efficiency of the bearings, whereas the rotor is affected by inertia forces that are so high as to determine severe vibrations of the supports.

Reluctance synchronous machines and drives

Abstract: 1. Brushless electric machines and drives: comparison criteria and results 2. Classification of reluctance synchronous machines and drives 3. Field distribution and inductance computation 4. Cageless rotor RSMs: identification and performance 5. Cage rotor RSMs: theory and performance 6. Driving control with motion sensors 7. Driving control without sensors 8. Generator mode 9. Machine design aspects Index

Ultrasound beam alignment servo

Abstract: A servo system for directing the operation of an ultrasound beam is described. The system includes a rotor and stator combination that utilizes electromagnetic forces to move the ultrasound beam in translational and rotational directions. In an embodiment of the invention the rotor is a permanent magnet that may be levitated and moved using a plurality of stator coils. Sensors are used to determine the position of the rotor, which information is used by a controller to regulate the stator operation designed to effect movement of the rotor. The sensors are preferably hall effect sensors. The permanent magnet is optionally placed in a fluid having buoyancy characteristics that reduce the electromagnetic force required to levitate the rotor. The rotor may be located off center within a housing so as to conform to asymmetrical viewing requirements, such as in transcranial Doppler ultrasound measurements.

Adaptive autocentering control for an active magnetic bearing supporting a rotor with unknown mass imbalance

Abstract: This paper presents a new approach, called adaptive autocentering, that compensates for transmitted force due to imbalance in an active magnetic bearing system. Under the proposed control law, a rigid rotor achieves rotation about the mass center and principal axis of inertia. The basic principle of this approach is to perform on-line identification of the physical characteristics of rotor imbalance and to use the identification results to tune a stabilizing controller. This approach differs from the usual strategy of adaptive feedforward compensation, which models the effect of imbalance as an external disturbance or measurement noise, and then cancels this effect by generating a synchronous reference signal. Unlike adaptive feedforward compensation, adaptive autocentering control is frequency independent and works under varying rotor speed. Performance of the control algorithm is demonstrated in simulation examples for the case of rigid rotors with static or dynamic imbalance.

Rotary machine with an electromagnetic rotary drive

Abstract: The rotary machine comprises a driven rotor (2) and an electric motor (4, 14) having a stator (4) and a driving rotor (14). The stator (4) is also executed as an electromagnetic bearing (4, 14) for the driving rotor (14), and the driving rotor (14) of the electric motor (4, 14) together with the driven rotor (2) of the rotary machine forms a rotor unit (2, 14), i.e. the two rotors (2, 14) form an integral rotor (2, 14). The rotary machine can for example be a rotary pump, a centrifugal pump, a centrifuge or a stirring apparatus. The rotor (2, 14) can be constructed so as to be easily removable from the stator (4).

Bearingless blood pump and electronic drive system

Abstract: A magnetically operated blood pump includes a rotor with an impeller that rotates within a housing, and the housing fastens to a driver that preferably electromagnetically controls the speed and disposition of the impeller in response to sensed conditions. The impeller and housing constitute a disposable assembly in which permanent magnets embedded in the impeller stabilize its position to maintain pumping tolerances in at least one dimension, and also couple to external fields to rotate the impeller. In one embodiment concentric arrangements of cylinder magnets passively maintain radial centering, while coils in the driver are actuated to simultaneously produce a rotational torque and to correct axial or tilt displacements. In a preferred embodiment of this type, sensors around the periphery detect axial displacement and/or tilt as the impeller turns, while the drive circuit responds to the sensor signal to produce compensating phase changes in the coil drive signals. The drive coils are disposed in a common plane and are symmetrically spaced about the central axis, and the phase changes in their drive signals result in a compensating axial force, which may be different in each of the coils to correct tilt. In another or further embodiment, the rotor is freely suspended such that blood washes over one or more surfaces of the rotor, and fluid pressure produces a net restoring force on the rotor to counteract changes in tilt or axial position within the housing. In this case, the driver need only drive rotation of the pump. The drive unit works with a variety of multipole impeller pumps, including ones with magnetic segmented rotors and conventional mechanical support bearings such as ones with a jewel or shaft bearing element. In other embodiments, plural sets of magnets provide passive constraint of radial disturbances and two tilt movements, while axial disturbances are corrected either passively by hydrodynamic surfaces or actively with the driver. The driver unit may include a hand crank assembly, enabling continued operation during power outages.

A nonlinear reduced order observer for permanent magnet synchronous motors

Abstract: This paper introduces a nonlinear reduced order observer for speed and rotor position estimation in permanent magnet synchronous motors (PMSMs). The observer is based on a model of the motor represented by stationary two-axes coordinates. The theoretical principles of the proposed observer are discussed. Sufficient conditions for convergence as well as convergence speed are established. The observer is designed and tested by simulation. The results show that the observer gives a good estimation of speed and rotor position. In addition, it has low sensitivity to torque disturbances and perturbations of the mechanical parameters.

Rotary electrical machines

Abstract: A rotary electrical machine (1) comprising a plurality of disc-shaped stator stages (3, 5, 7) and a plurality of disc-shaped rotor stages (2, 4, 6, 8), each of the rotor stages (2, 4, 6, 8) being respectively alternately interleaved with the stator stages (3, 5, 7). A space (94, 96) is provided between each stator stage and its adjacent rotor stage. Each of the stator stages is provided with at least two stator windings, defining a passage (82, 84) therebetween adjacent windings. A coiled pipe (100, 102 - Figures 3A and 3B) is disposed in or formed integrally with each of the passages (82, 84) in substantially the same plane as the stator stage, such that the outlet of one pipe (100) is coupled with the inlet of the pipe (102) disposed in the adjacent passage. In use, fluid, for example air, helium, water or oil is caused to flow around the coiled pipes (100, 102) in the passages between the stator windings. At the same time, cooling gas, for example, air or helium, is caused to pass through the stator-rotor spaces so as to cool the magnets (10), etc. and the retention hoops (18), etc. of the rotor stage as well as the outer surfaces of the stator stage. Alternatively, the stator-rotor spaces may be held under a vacuum.

Nonlinear control of active magnetic bearings: a backstepping approach

Abstract: In this paper, the authors utilize a nonlinear model of a planar rotor disk, active magnetic bearing system to develop a nonlinear controller for a full-order electromechanical system. The controller requires measurement of the rotor position, rotor velocity, and stator current and achieves global exponential rotor position tracking. Simulations are provided to illustrate the performance of the controller.

Methods for Speed Sensorless Control of AC Drives

Abstract: The operation of speed controlled ac drives with- out mechanical speed or position sensors requires the estima- tion of internal state variables of the machine. The assessment is based exclusively on measured terminal voltages and cur- rents. Low cost, medium performance sensorless drives can be designed using simple algebraic speed estimators. High-per- formance systems rely on dynamic models for the estimation of the magnitude and spatial orientation of magnetic flux waves in the stator or in the rotor. Open loop estimators and closed loop observers differ with respect to accuracy, robust- ness, and limits of applicability. The overview in this paper uses signal flow graphs of complex space vector quantities to give an insightful description of the physical and mathemati- cal systems used in sensorless ac drive control. I. INTRODUCTION AC drives based on full digital control have reached the status of a maturing technology in a broad range of applica- tions ranging from low-cost to high-performance systems. Continuing research has concentrated on the elimination of the speed sensor at the machine shaft without deteriorating the dynamic performance of the drive control system. Speed estimation is an issue of particular interest with induction motor drives where the mechanical speed of the rotor is generally different from the speed of the revolving magnetic field. The advantages of speed sensorless induction motor drives are lower cost, reduced size of the drive machine, elimination of the sensor cable, and increased reliability. A variety of different solutions for sensorless ac drives have been proposed in the past few years. This paper reviews their merits and limits based on a survey of the available litera- ture.

Sensorless rotor-position detection from zero to rated speed for an integrated PM synchronous motor drive

Abstract: By integrating the motor, the converter and the control circuits of electrical drives into one casing several advantages are obtained. The drive becomes compact, the amount of wiring is significantly reduced, and the control of the inverter and the motor can be designed to better utilize their respective characteristics. The paper presents an integrated permanent magnet synchronous motor drive (IPMSM) using complete digital control. The control includes a simple sensorless estimation of the rotor position both at standstill and at rotation. The algorithm for the initial rotor position detection is based on the saliency of the rotor at no load and it provides both the location as well as the direction of the magnetization. At rotation the rotor position is estimated by a predictor-corrector-based observer. The integrated concept makes it simple to include accurate values of the machine parameters.

An approach to real-time position estimation at zero and low speed for a PM motor based on saliency

Abstract: This paper presents a magnetic saliency based position estimation approach for a PM motor fed by a voltage-source PWM inverter. The proposed real-time estimation algorithm detects the motor current harmonics and calculates the inductance matrix including the rotor position information. The position estimation can be performed every period of pulse-width-modulation or carrier cycle. An experimental system using an interior permanent magnet (IPM) synchronous motor has been constructed. Experimental results verify that the position estimation within 10 degrees in electrical angle is obtained at standstill and such an extremely low-speed as 1 r/min by the proposed approach.

Blood collection and separation system

Abstract: The system includes a needle (72) (or other cannula-like device) for insertion into a vein of the donor and drawing whole blood therethrough, a variable-volume rotor (2a) for holding the blood after it is drawn, and a motor (50) for spinning the rotor so as to cause the blood to seperate into components, for example, plasma and red blood cells. The system also provides for a container for collecting a separated component. In a preferred embodiment two containers are used: the first container (92) for containing an anticoagulant, which is preferably added to the whole blood as it is drawn from the donor, and then for storing the plasma after it has been separated from the red blood cells, and the second container (91) for storing the separated red blood cells. The system further includes tubing (73), which may have valving (81) built into it and which may be acted on externally, so as to direct the blood components in the desired manner. The tubing connects the needle (72), the rotor (2a), and the first and second containers (92, 91). With the valving, the tubing is able to permit (i) the flow of whole blood from the needle (72) to the rotor (2a), (ii) the flow of anticoagulant from the first container (92) to the whole blood flowing from the needle to the rotor, (iii) the flow of plasma from the rotor to the first container, and (iv) the flow of red blood cells from the rotor to the second container (91). The motor (50) and the valving are preferably controlled by an electronic controller. Preferably, the system also includes a pump (61), which is also controlled by the controller, and which forces the blood components out of the rotor (2a) to the tubing. The pump is preferably able to draw the whole blood into the rotor.

Implantable electric axial-flow blood pump with blood-cooled bearing

Abstract: An axial-flow blood pump (10) has a rotor (20) suspended in ball-and-cup bearings (38, 34) which are blood-cooled but not actively blood-lubricated. The ball-and-cup structures are made of highly heat-conductive material and are in heat-transferring contact with heat-conductive stator blades (30) that serve as heat sinks for the bearings. The ball-and-cup structures are radially much smaller than the stator blades. The ball-to-cup interface has so small a gap that the ball-to-cup structures present an essentially continuous surface to the blood flow.

Rotary pump and process to operate it

Abstract: The invention concerns a rotary pump (3) having a housing (9) and a rotor (2) with blades (1b) which is placed inside the casing. The rotor (2) comprises a passive magnetically active rotor part (1) and the housing (9) is surrounded by a stator (7) having electrical windings (8a, 8b, 8c, 8d, 8e, 8f, 8g, 8h) and teeth (7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h). The stator (7) and the rotor part (1) form a motor that has no bearings, whereby the rotor part (1) can be actively controlled and operated by means of the electrical windings (8a, 8b, 8c, 8d, 8e, 8f, 8g, 8h) through three degrees of freedom. The rotor part (1) and the teeth (7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h) of the stator (7) are designed geometrically in a mutually adapted manner and are placed in such a way that the rotor part (1) is retained in the stator (7) through three additional degrees of freedom not actively controlled through passively operating reluctance forces, in order to mount the rotor (2) inside the housing (9) so that it can be driven and float frictionlessly.

Head rail-mounted actuator for window coverings

Abstract: A mini-blind actuator has a motor and a housing that holds the motor and a dc battery. The rotor of the motor is coupled to the baton of the mini-blind for rotating the baton and thereby opening or closing the slats of the mini-blind. Alternatively, the rotor is coupled to the tilt rod of the blind to rotate the tilt rod and thereby open or close the slats of the mini-blind. A control signal generator generates a control signal for completing the electrical circuit between the battery and the motor. The control signal can be generated in response to a predetermined amount of daylight or in response to a user-generated remote command signal. The actuator can be used to rotate the slats of horizontal or vertical blinds, or the sections of a pleated shade. Or, the actuator can be used to rotate the hollow rotatable tube of a roll-up shade.

A feasibility study of using smart materials for rotor control

Abstract: Rotor actuation in the rotating system promises a quantum jump in overall rotor craft performance. Smart material actuator technology for operation `on the blade' is now becoming available and has the potential to overcome the size, weight, and complexity issues of hydraulic and electric on-rotor actuation. The present paper is based on the results of a feasibility study to investigate the use of smart materials for primary and active control on the AH-64 helicopter. Based on the results of the study, it is seen that imbedded actuator concepts, i.e. pitch, twist, and camber control, are not practical at this time. Servoflap control, using hinged control surfaces driven by discrete actuators emerges as the most suitable candidate for smart material actuation. Preliminary data show that rotor control using smart materials might be feasible if a combination of smart materials is used and the rotor design is driven towards low control loads and motions.

Global stabilization of the oscillating eccentric rotor

Abstract: The oscillating eccentric rotor has been widely studied to model resonance capture phenomena occurring in dual-spin spacecraft and rotating machinery This phenomenon arises during spin-up as a resonance condition is encountered We consider the related problem of rotor despin Specifically, we determine nonlinear feedback control laws that not only despin the rotor but also bring its translational motion to rest These globally asymptotically stabilizing control laws are derived using partial feedback linearization and integrator backstepping schemes For the case in which the oscillating eccentric rotor is excited by a translational sinusoidal forcing function, the control law is shown to attenuate the amplitude of the translational oscillation

System and method for driving electric vehicle

Abstract: A T-S converter is composed of a first rotor which has a first control coil, a second rotor and a stator which has a second control coil. The second rotor has a first magnetic field member (such as permanent magnets) which supplies the first control coil with magnetic field and a second magnetic field member (such as permanent magnets) which supplies the second control coil with magnetic field. The first and second control coils are energized to drive the second rotor to rotate at a set speed with a set torque according to vehicle running condition. The first and the second control coil are also energized to generate battery charging current when the vehicle speed is decreased and the second rotor is driven by the vehicle wheels.

Cardiac support device

Abstract: An apparatus for pumping blood includes an elongated housing dimensioned to be at least partially positioned within the heart of a patient, a rotating member supported for rotational movement within the elongated housing and a drive mechanism for imparting rotational movement to the rotating member. The elongated housing includes an outer wall, a first inlet port for permitting blood to enter the elongated housing through a first end of the elongated housing and a second inlet port defined in the outer wall of the elongated housing for permitting blood to enter through the outer wall. The rotating member is rotatable to impart pumping energy to the blood entering through the first and second inlet ports to direct the blood through an outlet opening of the elongated housing. The rotating member preferably includes first and second blood pumping blade arrangements. The first blade arrangement is dimensioned to impart pump energy to the blood entering the elongated housing through the first inlet port. The second blade arrangement is dimensioned to at least impart pump energy to the blood entering the elongated housing through the second inlet port. The electric motor stator and rotor define a space therebetween through which blood entering the first inlet passes. The motor is an ironless core copper electromagnetic windings which provides a sufficiently large air space for blood flow.

Motor condition and performance analyzer

Abstract: A motor performance analyzer senses currents and voltages applied to the motor, converts the sensed signals to digital data signals, and stores the digital data signals. The analyzer includes a processor for evaluating the digital data and a display for alerting a user or technician to potential motor problems, or to developing problems, including winding faults and broken rotor bars. Advanced signal processing techniques are used to further evaluate stored data and to provide trending information.