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The torque produced by a synchronous reluctance machine (including the permanent-magnet-assisted machine) is studied analytically, with the aim of pointing out the effect of the position of the flux barriers on the torque ripple. It is verified that the position of the flux-barrier ends highly influences the torque waveform. With the aim of reducing torque harmonic contents, a new strategy is proposed based on the choice of couples of flux barriers of different shapes. The flux-barrier geometry is chosen so as to obtain a compensation between the torque harmonics produced by each couple. Experimental results on two prototypes confirm the analytical prediction. Index Terms--Low torque ripple, permanent-magnet (PM)-assisted synchronous reluctance machine, synchronous reluctance machine.

Recently, high-speed axial flux generator (HSAFG) has come to attention because of its some advantages such as high power density and efficiency. This paper presents a modeling and designing procedure of HSAFG with some details. The back iron of the permanent magnet is the main design subject investigated in this paper. Optimized thickness of the back-iron used in the rotor of two ends is determined for a HSAFG by carefully considerations of the terminal voltage, output power, and efficiency. These all vary by thickness of back-iron variation significantly. It is illustrated that a very small thickness of the rotor yoke reduces the terminal voltage and efficiency and a very large value of it increases the rotor inertia, mechanical problems and cost of the machine with no significant improvement of the machine performance characteristics. It is concluded that back-iron thickness of the rotor plays a singular and important role in the HSAFG and requires more carefully attention when designing the machine. Index Terms--Axial flux machine, coreless stator, high speed generator, rotor yoke thickness.

This paper presents an invention, the rotor position phase lock loop (PLL), which enables maximum power point (MPPT) tracking of wind by doubly-fed induction generators without needing a tachometer, an absolute position encoder, or an anemometer. The rotor position PLL is parameter variation insensitive, requiring only an estimate of the magnetization inductance for it to operate. It is also insensitive to noise in the electrical measurements. Proof of concept is by: 1) digital simulations and 2) experimental testing of a laboratory prototype. Index Terms--Decoupled P-Q control, doubly-fed induction generator (DFIG), maximum power point tracking, wind turbine generator (WTG).

Sensorless control of permanent-magnet synchronous machines (PMSMs) at low speed and standstill is often based on a difference between q- and d-axis inductances. By determining the inductances, i.e., by evaluating current responses that result from the supply of voltage test vectors, an estimation of the rotor position is obtained. These inductances are dependent on the stator current--because of (cross-)saturation--and on the geometry of the PMSM. Changing inductances strongly affect the accuracy of the rotor position estimation. This paper investigates the influence of geometrical parameters of the rotor on the inductances and on the position estimation. First, for several angles, widths, heights, and radial positions of the buried magnets in the rotor, finite element models (FEMs) calculate the inductances and the torque as a function of the stator current. Second, to study the effect of the variable q- and d-inductances on the position estimator, time-domain simulations are carried out in combination with FEM evaluations. The simulated control is validated on an experimental interior PMSM. The FEM is not needed by the controller in the experiments. Index Terms--Finite element analysis, permanent-magnet synchronous machines (PMSMs).

We have developed a 3-D finite-element mesh modification method for skewed motors with an auto-mesh generator. Meshes modified by the auto-mesh generator are broken as enlarging the skew angel. In order to solve this problem, we have improved the modification method by solving Laplace equation. In this paper, characteristics of the skewed squirrel-cage induction motor are analyzed by changing the rotor skew angle using the meshes created by the improved mesh modification method. Index Terms--Loss, skew, squirrel-cage induction motor, three-dimensional finite element method.

This study evaluates the potential benefits that fixed but deployable trailing-edge flaps may have on a low-twist hovering rotor using a blade-element method combined with two-dimensional and three-dimensional computational fluid dynamics. Low blade twist is beneficial in terms of forward-flight performance, which, combined with a deployable flap, could also offer good hover performance, resulting in an overall better design in comparison with a plain twisted blade. To evaluate this concept, a parametric study of flap configurations was conducted using a simple blade-element method based on computational-fluid-dynamics-generated two-dimensional aerodynamics. This simple model indicated that up to 6 deg of blade twist could be recovered at high rotor thrust by using an optimized flap configuration. Performance improvements were also obtained for outboard slotted-flap configurations. The optimum slotted-flap designs were also evaluated using three-dimensional computational fluid dynamics, which confirmed that an inboard flap combined with a low-twist (-7deg) rotor blade matched the performance of a plain blade with -13deg of twist. A blended-flap configuration was also applied and evaluated. This simpler design demonstrated the equivalent performance of a clean rotor with 10 deg of blade twist, providing further evidence of the potential of the fixed inboard flap concept.

This paper presents a case study of a design for a complete microair vehicle thruster. Fixed-pitch small-scale rotors, brushless motors, lithium-polymer cells, and embedded control are combined to produce a mechanically simple, high-performance thruster with potentially high reliability. The custom rotor design requires a balance between manufacturing simplicity and rigidity of a blade versus its aerodynamic performance. An iterative steady-state aeroelastic simulator is used for holistic blade design. The aerodynamic load disturbances of the rotor-motor system in normal conditions are experimentally characterized. The motors require fast dynamic response for authoritative vehicle flight control. We detail a dynamic compensator that achieves satisfactory closed-loop response time. The experimental rotor-motor plant displayed satisfactory thrust performance and dynamic response. DOI: 10.1061/(ASCE)0893-1321(2009)22:1(85) CE Database subject headings: Aerodynamics; Robotics; Dynamic response.

High-frequency current responses of a permanent magnet synchronous machine (PMSM), with and without considering eddy current effects, are significantly different. This paper investigates the eddy current effects on rotor position estimation. A compensation method is developed to improve the high-frequency-injection-based rotor position estimation of a PMSM at zero and low speeds. The paper also contributes to an improved magnetic pole identification based on space vector pulse width modulation for an arbitrary initial rotor position. The estimation and sensorless control method of PMSM, considering eddy current effects, has been verified by experimental results. Index Terms--Eddy current effects, initial rotor position, magnetic pole identification, permanent magnet synchronous machine (PMSM), rotor position estimation, sensorless control, space vector pulse width modulation (SVPWM).

Sensorless control of a permanent-magnet synchronous machine at low and zero speed is based on the injection of an oscillating high-frequency carrier signal. A particular demodulation technique serves to eliminate the estimation error introduced by pulsewidth modulation delay and the nonlinear characteristics of the inverter. Before the drive is started, the initial rotor position and the magnet polarity are detected. The initialization is performed by injecting an ac carrier and two short current pulses in a sequence. Index Terms--Initial rotor position, permanent magnet (PM) synchronous motor, sensorless control, zero-speed operation.

The relationship between the deviation of spin axis and the reflective optical intensity modulation and some related factors are analyzed. The results have shown that under the cryogenic environment the method using optical intensity modulation to measure spin-axis deviation is feasible.

A conceptual design of a superconducting rotor based on Mg[B.sub.2] conductor is designed for a synchronous machine. The overall machine design and parameters have shown a promising High Temperature Superconducting (HTS) flux pump excited double-helix design for synchronous machines.

A voltage-behind-reactance formulation of a synchronous machine model is set forth, which incorporates saturation and cross-saturation, and is general enough to encapsulate a variety of rotor structures by use of arbitrary linear networks instead of equivalent circuits. Specifically, the model's equations--originally expressed in the qd-axes framework--are rewritten in such a way as to allow the actual abc stator windings to be represented by inductive branches, which can then be naturally connected in the desired circuit topology, e.g., to a rectifier. The model's predictions are validated against experimental results. Index Terms--Electric machines, modeling, rotating machine transient analysis, simulation, synchronous generator transient analysis, synchronous machines, transfer functions.

This paper presents the modeling and steady-state performance of a novel dual-winding reluctance generator (DWRG) that uses a multiple-barrier (MB) rotor. A simple math-ematical model was developed, and the effects of external parameters (speed, field current, and load) on the steady-state performance were analyzed. Experimental results conducted on a prototype machine were also provided to justify the theoretical approach and performance calculations. The developed model takes into account the magnetic saturation and core loss and enables a quantitative prediction of load characteristics from the no-load test data. Index Terms--Core loss, dual winding, equivalent circuit, magnetic saturation, multiple-barrier (MB) rotor, reluctance generator.

In this paper, the definitions of rigid and flexible rotors, the rotor-dynamic analysis procedure, and the design criteria defined in the American Petroleum Institute (API) standard 541 are reviewed and compared to API 684. The definition of the quasi-flexible rotor is introduced, as it is not covered by the standards. The influence on critical speeds and response to unbalance of the parameters in the rotor-bearing system including foundation stiffness, bearing-support-structure stiffness, bearing-oil-film characteristics, and shaft design are analyzed for each type of rotor. The advantages and disadvantages of each type of rotor manufacturing, initial cost, maintenance, and possible site problems are also analyzed. Numerical results and test data are presented as study cases. The conclusion shows that it is important to know the operation conditions of the machine, specifically the operating-speed range and how the machine will be installed in order to select the most economical and reliable design for the particular case. If the machine will be constant speed, the question is less complex. The conclusion confirms that, in general, low-speed induction machines using standard plain cylindrical bearings and slower (up to 7000 kW) four-pole and high-speed (below 1000 kW) two-pole machines are well suited for rigid rotor design. Larger machines, particularly two-pole, are more practical to design as a flexible rotor. Adjustable-speed-drive machines introduce special concerns for the operation of flexible rotors when there is a critical speed in the operating range. Several design solutions are presented and discussed in terms of initial cost, maintenance, and performance. Index Terms--Flexible rotors, induction motors, rotor dynamic design.

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).sup.+] frame without involving positive/negative sequence decomposition whereas the auxiliary controller is implemented in the negative sequence [(dq).sup.-] 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. Index Terms--Control design, converter, doubly-fed induction generator (DFIG), modeling, unbalance, wind turbine.

This paper describes a novel generation rescheduling method to reduce the generator rotor shaft impacts induced by transmission loop closures. The rotor shaft impact constraints, at the instant of transmission loop closure, are explicitly modeled into an interior point optimal power flow. This method represents a considerable improvement on the conventional redispatch for reducing the standing phase angle of the closing breaker. Optimal power flow and transient stability results are provided for a tutorial four-bus and the IEEE 118-bus test systems. Index Terms--Benders decomposition, interior point methods, line closure, MW redispatch, optimal power flow, rotor shaft impact, standing phase angle, system restoration, transient stability, transmission loop.

Synchronous reluctance machines with solid rotor construction have advantages in certain high-speed applications such as flywheel energy storage systems. However, the solid rotor allows the flow of eddy currents, resulting in rotor loss and heat generation. The switching harmonics in the stator voltage supplied by a pulsewidth modulation (PWM) inverter are one of the sources of the rotor loss. This paper performs an analysis for the time harmonic loss in a solid-rotor synchronous reluctance machine, and investigates design and control issues associated with the inclusion of a three-phase LC filter for reduction of the rotor loss in solid rotor. A two-phase dynamic model of the machine which incorporates the LC filter dynamics is presented. This model is used to predict rotor losses due to switching harmonics generated by the three-phase PWM inverter. A model-based current regulator is utilized, which is modified to include the effects of the LC filter. Experimental results validate the proposed approach. Index Terms--filters, flywheels, harmonic analysis, losses, reluctance machines.

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. Index Terms--Drift and saturation, indirect vector control, model reference adaptive controller (MRAC), reactive power.

Inverters for medium voltage drives operate at re. duced switching frequency so as to restrain the dynamic losses of the power semiconductor devices. The resulting current harmonics can be reduced by synchronous optimal pulsewidth modulation (PWM), provided that steady-state conditions prevail. Transient conditions, however, interfere adversely with the optimal modulation patterns. Such conditions necessarily occur when the modulator forms part of a conventional closed-loop control scheme. Trajectory tracking control is employed to achieve high dynamic control in conjunction with synchronous optimal PWM. An optimal trajectory of the stator flux linkage vector is derived from the pulse pattern in actual use. The stator flux linkage vector is forced to follow this target trajectory. Modifying the target trajectory in transient conditions enables closed-loop torque control in a deadbeat fashion while conserving optimal modulation. Experimental results obtained from a 30-kW prototype drive operated at only 200 Hz switching frequency demonstrate the effectiveness of the approach. Index Terms--High-performance control, medium-voltage drive, rotor field orientation, synchronous optimal puisewidth modulation (PWM), trajectory tracking control.

This paper proposes a sensorless rotor temperature estimator for small- to medium-sized mains-fed induction machines. With measurements obtained only from voltage and current sensors, the proposed estimator can capture the rotor temperature online. The rotor speed is first extracted from the stator current harmonic spectrum based on the estimated rotor slot and eccentricity harmonic frequencies. Then the inductances are estimated according to the induction machine equivalent circuit developed from the rotor flux field orientation. The stator winding resistance at ambient temperature is the only motor parameter needed as input in this stage. Once the inductances are obtained, they are fed into the rotor resistance estimation algorithm to yield an estimate of the rotor resistance. Finally, the rotor temperature is calculated from the linear relationship between the temperature and rotor resistance. The experimental results from different motors are shown to validate the proposed algorithms. The whole scheme is efficient and reliable and is therefore suitable for implementation in a motor overload protection relay to provide thermal protection against rotor overheating. Index Terms--Condition monitoring, induction machines, motor parameter estimation, motor thermal protection, rotor resistance estimation, rotor slot harmonics, rotor speed detection.

The aim of this paper is to design and analyze reduced-order observers of the rotor flux of induction motors. The design is carried out in two steps. In the first step, a boundary of the stability region of the observation error is obtained corresponding to a chosen Lyapunov function. In the second step, the boundary is translated into a performance index that is minimized with respect to stator and rotor resistance variations and differences of voltages supplying the motor and those supplying the observer in order to obtain the largest stability region. Implementation of the observer on a low-cost fixed-point digital signal processor using look-up tables is described. Experimental results are shown with reference to a prototype consisting of a simple proportional--integral controller, the proposed observer, and a 2.2-kW induction motor; the implementations of both the controller and the observer are carried out on a DS1104 d-Space microcontroller using the fixed-point option. Index Terms--Induction motors, low-cost implementation, rotor flux observers.

An eccentric rotor creates an electromagnetic force between the rotor and stator of an electrical machine. This force tends to further increase the rotor eccentricity and may severely degrade the performance of the machine, causing acoustic noise, vibration, excessive wear of bearing, rotor and stator rubbing, and so forth. Parallel connections are known to be a simple yet effective remedy for the problems associated with rotor eccentricity. We have investigated two common types of electrical machines running with eccentric rotors. We examined operation over a wide whirling frequency range. We numerically evaluated and compared the effects of parallel connections in the stator and rotor windings on the eccentricity force. We found that the parallel stator windings can be more effective in mitigating the unbalanced magnetic pull than the rotor cage (or damper winding), which normally has many more parallel circuits. Index Terms--Finite-element methods, induction machines, synchronous generators, unbalanced magnetic pull, vibrations.

An experimental study of a rotatable tail mechanism applied to a small unmanned aerial vehicle was performed using a six-component wind-tunnel balance in the U.S. Air Force Institute of Technology low-speed wind tunnel. Attributes of the control and stability characteristics of the original vehicle, which were documented in an earlier study, are compared with those of a unique control methodology, a tail consisting of a single surface, with controllable elevation and rotation. An advantage of this change is a reduction in the storage length of the vehicle. Because there are similarities in the rotatable tail mechanism and the tail of many birds, the rotatable tail reflects a biomimetric feature. Measured force and moment coefficient measurements for the actual vehicle at a typical flight speed indicated that a rotatable tail provides a sufficient yaw moment for turning. For example, yaw moment coefficients [C.sub.n], ranging from -0.02 to +0.02, which is typical for a rudder, were achievable as long as the absolute value of the tail elevation angle was large. The dependence of the yaw moment coefficient on the elevator angle and angle of attack, in addition to the tail rotation angle, indicates that there would be significant challenges in applying a robust flight control scheme with the current actuator configuration. An additional feature of the tail design is that by deflecting the tail upward, it could also function effectively as an air brake. A more than twofold increase in drag coefficient for constant angle of attack was measured when the tail elevation angle was increased to nearly 70 deg. DOI: 10.2514/1.24192

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

We propose new concepts for the design, optimization, and control of a doubly salient permanent-magnet machine (DSPM). We employ a uniform pole width so that the width of the rotor pole is the same as that of the stator salient pole. This design aims to minimize the cogging torque. Second, we used a skewed rotor with one-half the pole width to improve the commutation. Finally, based on the flux linkage of the skewed rotor, we used a six-state commutating mode to control the motor. We validated the feasibility of these new design concepts by simulations, field analysis, and experimental measurements of the prototype. Index Terms--Cogging torque, commutating mode, doubly salient permanent-magnet machine (DSPM), pole width, skewed rotor.

This paper presents an analytical model of axial air gap induction motors with solid rotors that includes the two-dimensional current distribution in the rotor. The model is quasi-three-dimensional and considers the circumferential as well as radial and angular dimensions. Also, one can consider the various arrangements of the stator windings i.e., single layer, double layer, and gramme for this type of motor. The method is valid for both constant current and constant voltage sources. Comparison of the simulation results of the produced torque with the experimental ones shows the high accuracy of the proposed method. Index Terms--Analytical, axial air gap, induction machine, solid rotor.

The potential rotor heating in a 5 MW High Temperature Superconducting (HTS) Technology Demonstrator prototype motor is examined. Findings reveal the observation of measurable additional rotor heating with sea-state level-5 and motor speeds above 50 percent.

Aerodynamic and acoustic experiments were carried out to investigate the induced inflow distribution and noise characteristics of a scissors rotor in hover. The aerodynamic experiment was conducted on a model rotor rig and the induced inflows for two different scissors rotor configurations (the L configuration and U configuration) were measured. The experimental results indicate that the induced velocity near the lower blades is consistently larger than that near the upper blades. A free-wake analysis was used to predict the aerodynamic characteristics. The variation of the induced velocity with different scissors angles was simulated analytically and the results were compared with test data. The acoustic experiment was conducted in an anechoic aeroacoustic laboratory and the noise levels for both the scissors rotor configuration and a conventional configuration were measured. The effects of different scissors angles on rotor noise were investigated. It was shown that the noise level of a scissors rotor depends on both the azimuthal and vertical spacing and is not necessarily less than that of a conventional configuration.

The design and testing of an eight-pole superconducting rotating machine, which is based on an unconventional topology leading to an increase in power density, is presented. The Markov chain Monte Carlo (MCMC) method is used to calculate the magnetic scalar potential in selected regions of the discrete geometry.