Showing papers on "Rotor (electric) published in 1988"

Modeling of permanent magnet motor drives

Abstract: Research has indicated that the permanent magnet motor drives, which include the permanent magnet synchronous motor (PMSM) and the brushless DC motor (BDCM) could become serious competitors to the induction motor for servo applications. The PMSM has a sinusoidal back EMF and requires sinusoidal stator currents to produce constant torque while the BDCM has a trapezoidal back EMF and requires rectangular stator currents to produce constant torque. The PMSM is very similar to the wound rotor synchronous machine except that the PMSM that is used for servo applications tends not to have any damper windings and excitation is provided by a permanent magnet instead of a field winding. Hence the d, q model of the PMSM can be derived from the well-known model of the synchronous machine with the equations of the damper windings and field current dynamics removed. Because of the nonsinusoidal variation of the mutual inductances between the stator and rotor in the BDCM, it is also shown that no particular advantage exists in transforming the abc equations of the BCDM to the d, q frame. Hence the solution of the original abc equations is proposed for the BDCM. >

Noninvasive detection of broken rotor bars in operating induction motors

Abstract: A description is given of a computer-based noninvasive broken bar fault detector for squirrel-cage rotors of induction motors. The detector can be applied to existing motors without disassembly or shutdown and has the sensitivity to diagnose the presence of a single broken bar or an open end ring. It is suitable for monitoring the trend of the motor signature, or it can be used as a one-time diagnostic tool. >

Rotordynamics of Turbomachinery

Abstract: Introduction. Rotordynamic Considerations in Turbomachinery Design. Torsional Vibration Analysis. Critical Speeds and Response to Imbalance. Rotor Balancing in Turbomachinery. Bearings and Seals. Rotordynamic Instability in Turbomachinery. Measurements.

Implantable blood pump

Abstract: An implantable blood pump (10) for providing either continuous or pulsatile blood flow to the heart. The pump includes a stator (16) having a cylindrical opening (14), an annular array (36 or 38) of electromagnets (40, 42) carried by the stator concentric with the cylindrical opening and lying in a plane transverse to the axis (26) of the opening, a bearing (28) carried by the stator and extending across the cylindrical opening, and a rotor (12) supported by the bearing for rotation about the axis of the cylindrical opening, the rotor being in the form of an Archimedes screw and having a permanent magnet (48) in its periphery which lies in the same plane as the array of electromagnets. A controller (44) is provided which is capable of causing the array of electromagnets to be sequentially energized to cause the rotor to rotate. A heart beat sensing device (50) and a rotor speed sensing device (54) may be associated with the controller so the controller may vary the rotational speed of the rotor so that the output of the pump is varied between a high ouptut synchronized with a heart beat and a low output.

Calculation of Unsteady Wake/Rotor Interaction

Abstract: This paper presents a numerical analysis of wake/rotor interaction using a time-marching solution of the unsteady, nonlinear Euler equations. The incoming wakes are specified through the unsteady inflow boundary conditions. The lagged periodic boundary condition that arises due to unequal rotor/stator pitches is handled by a new technique that inclines the computational plane in time. Comparison of results for a flat-plate cascade with results using a linear analytic theory demonstrates the method's capability to accurately predict unsteady forces, moments, and radiated sound. Results are also presented for a low-speed turbine.

Induction motor analysis by time-stepping techniques

Abstract: A numerical approach is described that overcomes the deficiencies of other methods through the use of a two-dimensional, nonlinear, time-stepping finite-element method for excitation from a constant voltage source. Comparison of stator current for no-load and load conditions shows good agreement with test values on a large induction motor. It is shown that the method can provide a great deal of information on flux distribution and harmonic rotor bar currents. >

Composite wind turbine rotor blade and method for making same

Abstract: A wind turbine rotor blade including NASA LS (1) - 04xx airfoil sections having a twist not greater than 8° and a construction for such a blade which includes no parting line along the leading edge. The bond between a rectangular spar and the outer skin is reinforced by channels of "C" shaped cross section affixed to the skin and the spar. A method for manufacturing a rotor blade of this construction.

Alternating current generator

Abstract: An alternating current generator for supplying the electrical loads on a motor vehicle. The generator has a stator core that carries a three-phase stator or output winding. The rotor of the generator has two claw pole members that are so oriented that the fingers of the pole members are aligned. Disposed between the two pole members is a third pole member having projections disposed between the aligned fingers of the claw pole members. The rotor has two field coils which are so arranged and energized that the magnetic polarity of the two claw pole members is the same and opposite the magnetic polarity of the third pole member. One of the field coils can be replaced by a permanent magnet and when this is done the generator is provided with a magnetic circuit that can divert permanent magnet flux away from the stator core. Flux diversion is controlled by supplying unidirectional current to the field winding under the control of a voltage regulator.

A simple motion estimator for variable-reluctance motors

Abstract: A simple motion estimator for inverter-driven variable-reluctance motors is presented. The estimator probes unexcited phases with short voltage pulses from the inverter, and evaluates the resulting currents to measure the phase inductances. From these inductances, instantaneous motor position is estimated. Individual position estimates are optionally combined by a state observer to produce smoothed position and velocity estimates. Next, the secondary phenomena of eddy currents in the motor laminations, inverter switching noise, magnetic coupling between motor phases, and quantization introduced by digital implementation are all examined for their effects on estimator performance. Each phenomenon is addressed by a modification of the estimation. Finally, the estimator is evaluated experimentally using an inverter-driven three-phase motor having six stator poles and four rotor poles. The estimator is implemented digitally with an Intel 8031 microcomputer and little extra hardware. Further, it is embedded into a closed-loop controller of the inverter and motor. >

Application of sensor integration techniques to switched reluctance motor drives

Abstract: A novel drive system for a switched-reluctance (SR) motor is described. The system needs no position sensor and has no discrete current sensors for regulating phase currents. Instead, the drive uses power MOSFET transistors with integrated pilot devices for current feedback when the switches are 'off', a fixed off-time chopping strategy is used to control the phase currents. To eliminate the position sensor normally required for SR motor control, the controller estimates the rotor position using phase inductance measurements. This position estimation scheme is sufficiently precise to allow positioning of the phase firing pulses to within approximately two electrical degrees of the desired rotor angle, and full four-quadrant operation of the system is possible. A laboratory prototype system has been built and tested at speeds up to 3000 rpm. The system shows good performance in all four operating quadrants, including zero speed. The entire control for the system is implemented in a single low-cost microprocessor. >

Load enhancement effects due to polymer thickening in a short model journal bearing

Abstract: A model bearing is described which is 20.0 mm in diameter and 2.5 mm in length; a short bearing of diameter to length ratio eight. The clearance is large (500 μm) and the rotor may be run true or eccentric on its own shaft; in each case the mean load and frictional (tangential) force is measured as the centreline eccentricity is varied. Comparison is made between the lubricating performance of Newtonian and highly elastic liquids; the latter give load enhancement ratios of up to 300 and reductions in coefficient of friction by factors of the order 30. These effects are greatly in excess of those obtained when dealing with bearing of diameter to length ratio close to unity; possible reasons for this are discussed. A Newtonian oil and a polymer-thickened oil are tested in the same way, the latter oil is found to give load enhancement ratios of 1.4 (true rotor) and 3.5 (eccentric rotor) with corresponding reductions of coefficients of friction by factors of 1.5 (true rotor) and 3.0 (eccentric rotor). Such effects had not previously been observed when using oils in the internal cylinder geometry (journal bearing type) although somewhat similar effects have been found in the external cylinder and squeeze film geometries. The rheological properties of the polymer-thickened solutions are measured and the relevance of the results to friction and load bearing discussed.

Analysis of rotor failures in squirrel-cage induction motors

Abstract: The authors describe a procedure for analyzing rotor failures in squirrel-cage induction motors. They attempt to identify the various kinds of failure classes and patterns and relate them back to the probable cause of failure. They discuss five key areas that must be considered and related to one another in order to accurately diagnose the cause of rotor failure: failure class, failure pattern, appearance, application, and maintenance history. Finally, a summary of typical failures and tell-tale rotor appearances is presented. >

Method of manufacturing retention structure for electric motor rotor magnets

Abstract: An improved shaft mounted rotor assembly for an electric motor and method of manufacturing the same wherein a plurality of arcuate permanent magnets are positioned in angularly related adjacent positions to surround the outer periphery of a shaft mountable rotor core and a plastic molded sleeve encapsulates the exposed outer peripheral surfaces of the magnets to secure them in fast position on the core.

Efficiency-optimized flux trajectories for closed-cycle operation of field-orientation induction machine drives

Abstract: A structured design procedure for system integration is presented. A dynamic programming scheme is developed which optimizes efficiency of an induction-machine drive which is operated in closed-cycle and which has both control and state constraints. Application of rotor-flux feed-forward field-orientation control for an induction machine reduces the system equations to contain only three state variables: rotor flux, velocity, and position. Maximum stator current and rotor velocity are set as constraints. Saturation effects are modelled to provide a state-dependent constraint on the rotor-flux magnitude. Load is treated as a function of the rotor position, which is appropriate for many mechanical system applications. To optimize efficiency for closed-cycle operation of the motor, both machine losses as well as the cycle time must be minimized using an appropriate objective function. State trajectories of the system that simultaneously optimize machine efficiency and cycle time are found by dynamic programming. Flux trajectories for the optimal solution are found to vary significantly over the machine cycle. The validity of the energy optimization is investigated experimentally on a feedforward, field-oriented induction machine. >

Stator/rotor interaction in a transonic turbine

Abstract: This paper presents calculations of a stator/rotor interaction in a highly loaded transonic first turbine stage. Of particular interest is the propagation and reflection of shocks which originate at the trailing edge of the upstream stator. These produce a 40% variation in the lift on the rotor, which would cause structural vibrations and increased losses. Also, the unsteady shocks would cause temporary boundary-layer separation near the leading edge of the suction surface. The numerical procedure solves the inviscid unsteady Euler equations, including quasi-three-dimensional terms. The use of a conservative treatment guarantees the correct treatment of the moving shocks. A simple technique is used to couple the calculations on the stator and rotor grids. A key feature of the paper is the use of "time-incline d" computational planes to allow the analysis of cases in which the ratio of stator and rotor pitches is not equal to unity or the ratio of two small integers.

Magnetic bearing and suspension system

Abstract: A magnetic rotor suspension system including a magnetic rotor having a spin axis, and a generally spherical housing spaced from the rotor. The system includes means attached to the housing for applying magnetic fields to the rotor to fix its lateral and axial position relative to the housing and to adjust the angular orientation of the spin axis of the rotor relative to the housing.

Third harmonic commutation control system and method

Abstract: A system for determining rotor position information from the back emf of a permanent magnet motor includes extracting the third harmonic from the back emf of the motor by summing the terminal voltages of the motor. The phase angle of the third harmonic of the back emf is a function of the position of the rotor, and a signal is produced when the phase angle of the third harmonic (measured with respect to the voltage on the neutral conductor of the motor) reaches a predetermined angle. Electronically controlled switches selectively apply power to the phase windings of the motor in response to the detection of predetermined phase angles of the third harmonic.

Explicit Runge-Kutta method for unsteady rotor/stator interaction

Abstract: A quasi-three-dimensional rotor/stator analysis has been developed for blade-to-blade flows in turbomachinery. The analysis solves the unsteady Euler or thin-layer Navier-Stokes equations in a body-fitted coordinate system. It accounts for the effects of rotation, radius change, and stream-surface thickness. The Baldwin-Lomax eddy-viscosity model is used for turbulent flows. The equations are integrated in time using a four-stage Runge-Kutta scheme with a constant timestep. Results are shown for the first stage of the Space Shuttle Main Engine high pressure fuel turbopump. Euler and Navier-Stokes results are compared on the scaled single- and multi-passage machine. The method is relatively fast and the quasi-three-dimensional formulation is applicable to a wide range of turbomachinery geometries.

Method and apparatus for providing thermal protection for large motors based on accurate calculations of slip dependent rotor resistance

Abstract: A microprocessorized thermal protection system and accompanying method measures input voltage and current of an induction motor and derives therefrom continuously updated estimates of the slip dependent rotor resistance during acceleration of the motor. The measurements and calculations of the varying rotor resistance enable determination of the heat generated within the motor based on a thermal model thereof. Phase shift distortions induced by the measurement system are accounted for by determining the value of the stator resistance at start up. In addition, during a brief period following start up, sampling of the voltage/current inputs is suspended to avoid the effects of the initially occurring DC-offset resulting from the application of the voltage input to the inductive motor load.

System for adjusting radial clearance between rotor and stator elements

Abstract: The real-time adjustment system according to the invention utilizes an air flow regulating valve in an air conduit circuit activated by an output signal of an electronic computer. The computer determines a desired radial clearance at an operational time T of the gas turbine engine, which may be stored in the computer memory and may be based on a quantified engine model having the mechanical and thermal features of the rotor and stator elements which are to be controlled as function of engine thermodynamic parameters and the geometry of the elements, with the actual radial clearance computed in operation at the time T by the computer from data sensed in real-time and provided to the computer. The system also senses the maximum admissible stator temperature as well as the maximum temperatures and temperature gradients for the rotor. These limits are considered by the computer prior to emitting the output control signal to the valve. The output signal may also be modified by sensing the effect of the radial clearance by the tapping of the air flow from the compressor, by misalignment of the air between the rotor and stator elements and by the effect of the aerodynamic loses caused by the air tapped from the compressor on the specific consumption of the gas turbine engine.

Compound helicopter with no tail rotor

Abstract: This helicopter invention uniquely has no anti-torque tail rotor. The tail propeller is used only for forward thrust during the airplane mode of flight and during the transition from vertical helicopter flight to forward airplane mode of flight, when the helicopter rotor may be feathered in a no-lift attitude. The anti-torque balancing forces during the hovering mode are developed by the differentially controlled aileron forces when the wings are aligned vertically with the vertically downward airflow from the helicopter rotor. There is also a vertically moveable horizontal airfoil on the tail cone, or tail boom, with controllable means which can provide anti-torque reaction forces during the helicopter hovering mode from the lifting rotor down flow air. An angular moveable tail fin assembly and rudder are provided to improve transition from VTOL hovering flight to horizontal airplane flight. Means are provided to electronically schedule transition from the VTOL to horizontal cruise flight sensed by the wing attitude which can control the angular attitude of the fin and rudder in a completely computerized automatic transition to and from VTOL and airplane flight mode.

Labyrinth seal system

Abstract: A labyrinth seal system for reducing leakage flow of a compressible fluid between a rotating portion of a machine rotating relative to a stationary portion of the machine. A stator seal element is connected to the stationary portion of the machine and a rotor seal element is connected to the rotating portion of the machine. The rotor seal element defines a plurality of staggered cavities. Straight long teeth connected to the stator seal element define throttling clearances with the bottom walls of the staggered cavities of the rotor seal element, and short teeth connected to the stator seal element slanted upstream relative to the direction of leakage flow define throttling clearances with the rotor seal element. Undercuts can optionally be defined by the rotor seal element on the downstream side of the cavities. Optional straight teeth connected to the rotor seal element downstream of the cavities define throttling clearances with the stator seal element. The short teeth of the stator seal element can optionally be straight. Optionally all the teeth can be slanted in the direction of leakage flow. The configurations of the rotor seal element and the stator seal element can be reversed.

Turbine rotor retention system

Abstract: Damping of a turbine rotor is attained by a weighted member trapped between pockets formed in the neck of adjacent blades at one end and a space between the disk and TOBI rotor seal and forward extending blade lug at the other end. The feather seal which is a curved plate fits over the top of the weighted member and is trapped between nubs formed on the front and rear underside of the blade platform. The front face of the rim of the disk at the disk cavity is open ended and blocked off at the rear face. This assembly allows for individual blade removal and viewing from the rear face by removing a single rim cavity cover without disturbing the remaining components of the assembly. The inverted ring supports take up the axial loads alleviating the loads heretofore taken up by the TOBI rotor seal, allowing for a lighter weight installation.

High-speed torque control of brushless permanent magnet motors

Abstract: A method of converter control that improves the high-speed torque of brushless permanent-magnet (PM) motors is presented. The method consists of modulating the converter conduction intervals and their phase relative to the rotor position in order to deliver current to the stator windings at high speeds where the motor back EMF approaches the convertor rating. A microprocessor-based controller is used in the implementation. With this control, operation of the PM motor drive at its maximum ratings can be extended to higher speeds. >

Pulsating hot and cold shower head

Abstract: The shower head dispensing device simultaneously dispenses a plurality of separate liquids in pulsating simultaneous streams. The liquid streams are maintained separate within the device by the use of separate distribution chambers, channels and nozzle sections. A free-turning, tiered rotor is provided within the device. The rotor turns on frictionless bearings provided by hydraulic balancing of the liquid pressures around the rotor. The liquid flow is maintained separate within the device and rotor and provides pulsating liquid flow through the tiers of the rotor and out through outlet openings provided in the device. Angularly adjustable nozzles are proivided within the nozzle sections and adjacent to each tier of the rotor so that the pressurized liquids flowing through the nozzles will impinge upon the outer perimeter of the rotor causing the rotor to rotate as the desired speeds. The speed of the rotor determines the time differential between the pulses present in each of the simultaneously dispensed liquids.