Showing papers on "Rotor (electric) published in 1997"

A direct torque controlled interior permanent magnet synchronous motor drive incorporating field weakening

Abstract: This paper presents a new control scheme for wide speed range operation of interior permanent magnet synchronous motor drives, where both torque and stator flux linkage are directly controlled. The proposed scheme possesses some attractive features when compared to the conventional current-controlled drives. Current controllers followed by pulsewidth modulation or hysteresis comparators and coordinate transformation are not used. This eliminates the delays through these networks and offers the possibility of dispensing with the rotor position sensor for the electronic commutator, if the initial rotor position is known only approximately. The scheme incorporates all the usual control regimes, such as the maximum torque per ampere operation in constant torque region, the flux-weakening region, and operates the drive within the voltage and current limits of the motor/inverter. The control scheme has been verified by simulation and experimental tests with a prototype interior magnet motor. This paper describes the scheme in detail, followed by results of its implementation.

Process and apparatus for achieving power augmentation in gas turbines via wet compression

Abstract: A power augmentation apparatus and process for effectively adding a mass flow of water to the working fluid acquired by the compressor of an industrial gas turbine, and especially for adding a mass flow of water to a fully-humidified working fluid for reducing the work of compression performed by the compressor and achieving a net augmentation of the power produced by the turbine, said apparatus and process preferably including the use of a spray rack group assembly having at least one spray rack water pipe and at least one spray rack water nozzle which assembly is ideally positioned a distance away from the compressor inlet. Water mass flow is added preferably in increments which correspond to the spray rack water pipes and associated nozzles. Monitoring of the temperature profile of fluid-cooled rotor blades in the turbine section with an optical pyrometer to detect clogging of cooling pathways in those rotor blades from impurities in the added water, monitoring of the working fluid's temperature in proximity to the gas turbine compressor inlet to guard against the possibility of icing, a deformation measurement device, and concurrent addition of heat and humidity, preferably steam, to the working fluid as a means to extend the utility of the process and apparatus to lower ambient air temperature operation are disclosed.

Effect of Squealer Tip on Rotor Heat Transfer and Efficiency

Abstract: Calculations were performed to simulate the tip flow and heat transfer on the GE-E 3 first-stage turbine, which represents a modern gas turbine blade geometry. Cases considered were a smooth tip, 2 percent recess, and 3 percent recess. In addition, a two-dimensional cavity problem was calculated. Good agreement with experimental results was obtained for the cavity calculations, demonstrating that the k-ω turbulence model used is capable of representing flows of the present type. In the rotor calculations, two dominant flow structures were shown to exist within the recess. Also areas of large heat transfer rate were identified on the blade tip and the mechanisms of heat transfer enhancement were discussed. No significant difference in adiabatic efficiency was observed for the three tip treatments investigated.

Implementation and position control performance of a position-sensorless IPM motor drive system based on magnetic saliency

Abstract: This paper describes position-sensorless control of an interior permanent magnet synchronous (IPM) motor, which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm detects motor current harmonics and determines the inductance matrix, including rotor position information. An experimental system consisting of an IPM motor and a voltage-source pulsewidth modulation inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms.

Torque ripple minimization in switched reluctance motors using adaptive fuzzy control

Abstract: An adaptive fuzzy control scheme for torque ripple minimization of switched reluctance machines (SRM) is presented. The fuzzy parameters are initially chosen randomly and then adjusted to optimize the control. The controller produces smooth torque upto the motor base speed. The torque is generated over the maximum positive torque producing region of a phase. This increases the torque density and avoids high current peaks. The controller is robust towards errors in the rotor position information which means inexpensive crude position sensors can be used. Detailed simulation and experimental results are presented. The controller shows good response in both cases.

Dynamics of Forced Nonlinear Systems Using Shooting/Arc-Length Continuation Method—Application to Rotor Systems

Abstract: The analysis of systems subjected to periodic excitations can be highly complex in the presence of strong nonlinearities. Nonlinear systems exhibit a variety of dynamic behavior that includes periodic, almost-periodic (quasi-periodic), and chaotic motions. This paper describes a computational algorithm based on the shooting method that calculates the periodic responses of a nonlinear system under periodic excitation. The current algorithm calculates also the stability of periodic solutions and locates system parameter ranges where aperiodic and chaotic responses bifurcate from the periodic response. Once the system response for a parameter is known, the solution for near range of the parameter is calculated efficiently using a pseudo-arc length continuation procedure. Practical procedures for continuation, numerical difficulties and some strategies for overcoming them are also given. The numerical scheme is used to study the imbalance response of a rigid rotor supported on squeeze-film dampers and journal bearings, which have nonlinear stiffness and damping characteristics. Rotor spinning speed is used as the bifurcation parameter, and speed ranges of sub-harmonic, quasi-periodic and chaotic motions are calculated for a set of system parameters of practical interest. The mechanisms of these bifurcations also are explained through Floquet theory, and bifurcation diagrams.

A Survey of Theoretical and Experimental Coaxial Rotor Aerodynamic Research

Abstract: The recent appearance of the Kamov Ka-50 helicopter and the application of coaxial rotors to unmanned aerial vehicles have renewed international interest in the coaxial rotor configuration. This report addresses the aerodynamic issues peculiar to coaxial rotors by surveying American, Russian, Japanese, British, and German research. (Herein, 'coaxial rotors' refers to helicopter, not propeller, rotors. The intermeshing rotor system was not investigated.) Issues addressed are separation distance, load sharing between rotors, wake structure, solidity effects, swirl recovery, and the effects of having no tail rotor. A general summary of the coaxial rotor configuration explores the configuration's advantages and applications.

The effects of PWM voltage source inverters on the mechanical performance of rolling bearings

Abstract: Modern power inverters provide the industrial control industry with significant advantages. The faster switching devices have increased drive performance, but with some disadvantages. One disadvantage, rotor shaft voltage and resulting bearing current, has become an industry concern. The oil film in a bearing acts as a capacitor and provides a charging mechanism for rotor shaft voltage buildup. Electrical breakdown of the film can damage the bearing. This paper examines the mechanical and electrical characteristics of the bearing and converts them into models. The mechanical model for the bearing contact area establishes an allowable bearing current density, which is used to estimate the electrical life of a mechanical bearing. The electrical model for the bearing provides a significant advancement, aids bearing design, and the analysis of electrically induced bearing damage. Finally, the paper presents quantitative results for one solution to the shaft voltage and bearing current problem.

Initial rotor angle detection of a nonsalient pole permanent magnet synchronous machine

Abstract: This paper presents a technique that calculates the absolute angular position of a permanent magnet (PM) rotor within a pole pair at standstill. The algorithm works with nonsalient pole motors. By choosing an appropriate voltage pulse width and applying it to each phase winding, the stator currents partially saturate the stator iron, enabling the algorithm to discern between a north pole and a south pole, and subsequently, the absolute position. The scheme is computationally simple and does not rely on the knowledge of any of the motor parameters.

Modeling and simulation of induction machine vector control with rotor resistance identification

Abstract: This paper shows that it is possible to use available commercial software to model and simulate a vector-controlled induction machine system. The components of a typical vector control system are introduced and methods given for incorporating these in the MATLAB/SIMULINK software package. The identification of rotor resistance is important in vector control, if high-performance torque control is needed, and modeling of the extended Kalman filter (EKF) algorithm for parameter identification is discussed. It is certainly advisable, when feasible, to precede implementation of new algorithms, whether for control or identification purposes, with an extensive simulation phase. Additionally, a technique for generating pulse-width modulation (PWM) phase commands to extend machine operation to higher speeds before field weakening occurs is simulated in a vector-controlled induction machine, driven by a PWM inverter. This demonstrates the versatility of the vector-controlled induction machine system model.

Induction motors thermal monitoring by means of rotor resistance identification

Abstract: Rotor and stator temperature are of concern in both short-term machine protection and in longer term condition monitoring for large induction machines. Especially, when operating with overload cycles, it is necessary to monitor rotor bars and stator winding temperatures to make sure that the temperature remains below prescribed limits. The purpose of this paper is to present a thermal monitoring technique, for induction motors steady-state operation, based on the rotor resistance identification. Experimental results, for a 4 kW four-pole squirrel cage induction motor, show the industrial viability of the proposed technique.

Lessons from rotor 37

Abstract: NASA rotor 37 was used as a ‘blind’ test case for turbomachinery CFD by the Turbomachinery Committee of the IGTI. The rotor is a transonic compressor with a tip speed of 454 m/s (1500 ft/s) and a relatively high pressure ratio of 2.1. It was tested in isolation with a circumferentially uniform inlet flow so that the flow through it should be steady apart from any effects of passage to passage geometry variation and mechanical vibration. As such it represents the simplest possible type of test for three-dimensional turbomachinery flow solvers. However, the rotor still presents a real challenge to 3D viscous flow solvers because the shock wave-boundary layer interaction is strong and the effects of viscosity are dominant in determining the flow deviation and hence the pressure ratio. Eleven ‘blind’ solutions were submitted and in addition a ‘non-blind’ solution was used to prepare for the exercise. This paper reviews the flow in the test case and the comparisons of the CFD solutions with the test data. Lessons for both the Flow Physics in transonic fans and for the application of CFD to such machines are pointed out.

Method and apparatus for providing high bandwidth force feedback with improved actuator feel

Abstract: A method and apparatus for providing low-cost, realistic force feedback including an improved actuator. Force sensations are provided to a user and an interface device coupled to a host computer allows a user to interact with a host application program. A user object, such as a joystick, is moveable by a user in at least one rotary degree of freedom. A sensor reports a locative signal to the host computer to indicate a position of the user object. An actuator outputs forces on the user object in response to signals from the host computer and program. The actuator includes a housing, a set of grounded magnets provided on opposing surfaces of the housing and creating a magnetic field, and a rotor coupled to the user object positioned between the magnets. The rotor rotates about an axis of rotation and includes a shaft and teeth spaced around the shaft. An electric current flows through one or more coils on the teeth to cause the rotor to rotate. The teeth and the magnets are provided in a skewed, helical arrangement relative to each other so that, as the rotor rotates, a first tooth gradually exits the magnetic field as the next consecutive tooth gradually enters the magnetic field, thereby significantly reducing a cogging effect of the rotor when the user object is moved by the user and increasing the fidelity of forces experienced by the user.

Control circuit for five-phase brushless dc motor

Abstract: A control system (100) for a five-phase brushless DC motor (102) including a stator having five windings and a rotor (116) mounted for rotation relative to the windings (114). The windings (114) are adapted to be electronically commutated in response to the rotary position of the rotor (116). The control system (100) includes a sensing circuit (106) to sense the rotary position of the rotor (116) using an optical or magnetic sensor or the back electromotive force voltages in the windings (114). Electronic switches (112) control the flow of current through the windings (114) in response to control signals generated by a control circuit (110) in response to the rotary position of the rotor (116). The control circuit (110) includes start-up logic to start the motor (102). If the rotor (116) is rotating in a wrong direction upon start-up, the control circuit (110) energizes preselected windings (114) and waits for the movement of the rotor (116) to come substantially to a stop and then energizes the windings (114) in a start-up sequence to cause the rotor (116) to rotate in a correct direction. Once the rotor (116) is rotating in the correct direction, the control circuit (110) electronically commutates the windings (114) in response to the rotary position of the rotor (116).

Motor control circuit

Abstract: A motor controller for regulating the application of current to the windings of a motor in order to both control the actuation of the motor rotor and the braking of the rotor. The motor controller includes a speed control circuit regenerating a signal representative of the user-selected speed, a direction controller to signal if the motor is to be driven in the forward, reverse or oscillatory motion and a speed override circuit. There is also a current sensor for monitoring the current drawn by the motor, a brake controller and an energization circuit. The energization circuit regulates the application of a current to the motor to cause the rotation or braking of the rotor. When the motor is to be oscillated, each time the direction controller circuit transitions a FORWARD/REVERSE signal, the speed override circuit causes the energization circuit to momentarily apply energization signals to the motor based on the application of a zero-speed, user-speed signal. During such transitions, the current sensor sends a signal to the energization controller to make it appear that the motor is drawing in a large amount of current. Whenever the motor is operating at a speed higher than the user-speed, the brake controller causes the energization controller to apply braking current to the motor. However, if the rotor is not turning, the brake controller inhibits the assertion of the braking current.

Nonlinear Dynamics of a Rigid Unbalanced Rotor in Journal Bearings. Part I: Theoretical Analysis

Abstract: The dynamic behaviour of a rigid rotor supported on plain journal bearings was studied, focusing particular attention on its nonlinear aspects Under the hypothesis that the motion of the rotor mass center is plane, the rotor has five Lagrangian co-ordinates which are represented by the co-ordinates of the mass center and the three angular co-ordinates needed to express the rotor's rotation with respect to its center of mass In such conditions, the system is characterised not only by the nonlinearity of the bearings but also by the nonlinearity due to the trigonometric functions of the three assigned angular co-ordinates However, if two angular co-ordinates have values that are generally quite small because of the small radial clearances in the bearings, the system is de facto linear in these angular co-ordinates Moreover, if the third angular co-ordinate is assumed to be cyclic [18], the number of degrees of freedom in the system is reduced to four and nonlinearity depends solely on the presence of the journal bearings, whose reactions were predicted with the π-film, short bearing model After writing the equations of motion in this way and determining a numerical routine for a Runge–Kutta integration the most significant aspects of the dynamics of a symmetrical rotor were studied, in the presence of either pure static or pure couple unbalance and also when both types of unbalance were present Two categories of rotors, whose motion is prevailingly a cylindrical whirl or a conical whirl, were put under investigation

Swept fan blade

Abstract: A swept blade design for the low pressure compressor rotor or fan of a ducted fan gas turbine engine has a leading edge which is inclined relative to an axial direction of airflow through the rotor stage. The sweep angle varying with blade, span height from the rotor axis has a negative or forward sweep near the rotor hub, changing to a positive or rearward sweep as span height increases, changing again near the tip to negative or forward sweep.

Method and apparatus for controlling a brushless DC motor that indicates a motor failure

Abstract: A method and apparatus for controlling a brushless DC motor which has a permanent magnet rotor and a 3-phase stator winding for applying a rotating magnetic field to the permanent magnet rotor. A specified reference voltage is compared with the stator winding terminal voltages for each phase. The rotor position is detected from the output of these comparison circuits based on the induced voltages generated in the stator windings which are not conducting when the motor is rotated. The stator windings which conduct current are controlled in response. Furthermore, a specific conduction pattern is supplied to each stator winding when the rotor is stopped, and a reference output determined for the conduction pattern is compared with the output of the comparison circuits when the stator windings are conducting. Abnormalities are detected based on the comparison results of the comparison circuit.

Key Results from a Higher Harmonic Control Aeroacoustic Rotor Test (HART)

Abstract: In a major cooperative research program within existing US-German and US-French Memoranda of Understandings (MoU's) a comprehensive experimental study was conducted with a 40-percent geometrically and dynamically scaled BO-105 main rotor operated in the open-jet-anechoic test section of the German-Dutch Wind Tunnel (DNW). The objectives of the program were to improve the physical understanding and the mathematical modelling of the effects of the higher harmonic blade pitch control technique on blade-vortex interaction (BVI) impulsive noise and vibration reduction. A unique set of acoustic, dynamic, dynamic response, performance, and rotor wake data were acquired with a pressure and strain gauge instrumentedblade and by application of non-intrusive measurement techniques. This paper is focused on the experimental part of this research program, termed Higher-harmonic-control Aeroacoustic Rotor Test (HART) which was jointly performed by researchers from the.

Field-oriented control of an induction motor with robust on-line tuning of its parameters

Abstract: This paper proposes new torque control of an induction motor, which is robust against primary resistance and adaptable to leakage inductance, magnetizing inductance, and secondary time constant. The control is based on flux feedback with a flux simulator. Since the simulator is based on a rotor current model, it is independent of the primary resistance, but uses the magnetizing inductance and secondary time constant values to estimate the flux. Parameter mismatch in the simulator detrimentally affects flux and torque responses. In order to compensate for degradation of the responses, an identifier for the magnetizing inductance and the secondary time constant is introduced. The identifier is insensitive to the primary resistance because it is based on instantaneous reactive power of the motor. Also, a leakage inductance identifier is introduced to achieve perfect compensation, which is robust against other parameters owing to instantaneous harmonic reactive power. To verify feasibility of the proposed technique, digital simulations and experimental tests have been conducted. The results have proven excellent characteristics of the drive system, which confirms validity of the scheme.

The effect of rotor design on sensorless speed estimation using rotor slot harmonics identified by adaptive digital filtering using the maximum likelihood approach

Abstract: Adaptive digital filtering has been demonstrated as an effective technique for extracting a real-time, sensorless, speed signal from rotor slot harmonics (RSHs) embedded in the line current waveform of induction motor drives. It is known that sensorless speed estimation techniques using RSHs may exhibit poor performance with certain motor designs. This paper examines the reasons for that poor performance which reflects differences in the magnitude of the slot harmonic signals consequent upon rotor design. Experimental results for a 30 kW motor with 6 different rotors are presented. The significant parameters are the number of rotor slots, skew and the accuracy of construction. It is clearly shown how inferior performance can arise. Conversely, improvements in reliability of speed estimation and transient response can be obtained by recognising those aspects which provide an enhanced signal, by minimising the background noise of the inverter/machine, or by enhancing the adaptive filter. The recursive maximum likelihood technique is presented as an improved algorithm for tuning the digital filter which aids transient response and reliability of speed estimation. Real time, experimental transient performance is demonstrated for the different rotors used in this paper and the performance failure of a particular slot combination demonstrated.

Blockage Development in a Transonic, Axial Compressor Rotor

Abstract: A detailed experimental investigation to understand and quantify the development of blockage in the flow field of a transonic, axial flow compressor rotor (NASA Rotor 37) has been undertaken. Detailed laser anemometer measurements were acquired upstream, within, and downstream of a transonic, axial compressor rotor operating at 100%, 85%, 80%, and 60% of design speed which provided inlet relative Mach numbers at the blade tip of 1.48, 1.26, 1.18, and 0.89 respectively. The impact of the shock on the blockage development, pertaining to both the shock / boundary layer interactions and the shock / tip clearance flow interactions, is discussed. The results indicate that for this rotor the blockage in the endwall region is 2–3 times that of the core flow region, and the blockage in the core flow region more than doubles when the shock strength is sufficient to separate the suction surface boundary layer.Copyright © 1997 by ASME

Minimising rotor losses in high-speed high-power permanent magnet synchronous generators with rectifier load

Abstract: In an early stage of the design of a high-speed 1400 kW synchronous generator with permanent magnet excitation and loaded by a rectifier, it became apparent that rotor losses are a major problem. The stator currents cause asynchronous components in the air-gap field. Analysis shows that a modified polyphase system reduces the number of these components. An approximate solution for the rotor losses caused by the asynchronous field components has been derived. The formulae show the effects of machine dimensions and harmonics and the effect of a conducting shield in the rotor. The main purpose of the study is to have a tool for making an early choice among several stator winding configurations. A modified nine-phase system, combined with a shield around the permanent magnet rotor, is a prospective option.

The Acoustic Influence of Cell Depth on the Rotordynamic Characteristics of Smooth-Rotor/Honeycomb-Stator Annular Gas Seals

Abstract: A two-control-volume model is employed for honeycomb-stator/smooth-rotor seals, with a conventional control-volume used for the throughflow and a capacitance-accumulator model for the honeycomb cells. The control volume for the honeycomb cells is shown to cause a dramatic reduction in the effective acoustic velocity of the main flow, dropping the lowest acoustic frequency into the frequency range of interest for rotordynamics. In these circumstances, the impedance functions for the seals cannot be modeled with conventional (frequency-independent) stiffness, damping, and mass coefficients. More general transform functions are required to account for the reaction forces, and the transfer functions calculated here are a lead-lag term for the direct force function and a lag term for the cross-coupled function. Experimental measurements verify the magnitude and phase trends of the proposed transfer functions. These first-order functions are simple, compared to transfer functions for magnetic bearings or foundations. For synchronous response due to imbalance, they can be approximated by running-speed-dependent stiffness and damping coefficients in conventional rotordynamics codes. Correct predictions for stability and transient response will require more general algorithms, presumably using a state-space format.

Sensorless, online motor diagnostics

Abstract: Early detection of abnormalities in electric motors helps to avoid expensive failures. Motor current signature analysis (MCSA) implemented in a computer-based motor monitor can contribute to such condition-based maintenance functions. Such a system may also detect an abnormality in the process as well as the motor. Extensive online monitoring of the motors can lead to greater plant availability, extended plant life, higher quality product, and smoother plant operation. With advances in digital technology over the last several years, adequate data processing capability is now available on cost-effective, microprocessor-based, protective-relay platforms to monitor motors for a variety of abnormalities in addition to the normal protection functions. Such multifunction monitors, are displacing the multiplicity of electromechanical devices commonly applied for many years. Following some background information on motor monitoring, this article features recent developments in providing tools for the diagnosis of faults or incipient faults in electric motor drives, including: sensorless torque measurement; direct detection of turn-to-turn short circuits; detection of cracked or broken rotor bars; and detection of bearing deterioration.

Current model-based sensorless drives of salient-pole PMSM at low speed and standstill

Abstract: For all the sensorless drives of the permanent magnet synchronous motor (PMSM), the major problem exists in their low-speed operation. This paper gives a solution to this problem by using a salient-pole PMSM. At low speeds, including zero speed, the rotor position and speed can be estimated by the current response of the voltage pulse, which is intermittently applied to the current minor loop. The current response is position dependent, because the winding inductance is a function of the rotor position. By using the relation between the current response and the rotor position, the basic algorithm of the sensorless drive can be developed. Experimental results from a six-pole 1500 RPM 1.5 kW test motor have proved the stable sensorless drive characteristics below 50 RPM, including zero speed, under 0%-100% loaded conditions.

Design and analysis of high-speed brushless permanent magnet motors

Abstract: The paper reports on the design of a 20000 rpm, 3-phase brushless permanent magnet DC motor for use in a friction welding unit, in which studs up to 3 mm diameter are welded by coordinating the rotational speed of the motor with the force applied by a linear permanent magnet servo-actuator. The motor consists of a stator having 3 teeth, which carry nonoverlapping windings, and a 2-pole diametrically magnetised sintered NdFeB magnet rotor. The air gap flux density distribution is essentially sinusoidal. The advantages and disadvantages of such a motor topology for this and other high speed applications are discussed, and an optimal air gap diameter is derived. The effect of the stator tooth tip geometry on the waveform of the induced EMF is investigated by finite element analysis, and validated by measurements, whilst the merits of laminated silicon iron and soft magnetic composite materials for the stator core are considered.

Electromagnetic machine with at least one pair of concentric rings having modularized magnets and yokes

Abstract: An electromagnetic machine which is suitable for use as a direct-drive, directly-coupled, mains electricity generator (14) to be driven by a low speed device such as a wind turbine (18), consists of one or more rotor rings (30) of many permanent magnets (40) of alternating polarity, with coaxial stator rings (28) of many laminated yokes (35), each yoke defining slots to locate coils (38). The yokes (35) and coils (38) form modules which are supported by beams (32) relative to the rotor rings (30). The rotor rings (30) may also be of modular construction. Manufacture and assembly are thereby simplified, and sub-harmonic magnetic flux components are suppressed.