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Active magnetic bearing (AMB) becomes widely used in various kinds of rotating machinery. However, as the magnetic force is nonlinear, nonlinear phenomena may occur when the rotating speed becomes high and delays of electric current or magnetic flux in the AMB relatively increase. In this paper, the magnetic force in the AMB is modeled by considering both the second-order delay of the electric current and the first-order delay of the magnetic flux. The magnetic flux in the AMB is represented by a power series function of the electric current and shaft displacement, and its appropriate representation for AMB is discussed. Furthermore, by using them, the nonlinear theoretical analysis of the rigid rotor system supported by the AMB is demonstrated. The effects of the delays and other AMB parameters on the nonlinear phenomena are clarified theoretically, and they are confirmed experimentally. [DOI: 10.1115/1.3172139]

The rotor-active magnetic bearing system subjected to a periodically time-varying stiffness having quadratic and cubic nonlinearities is studied and solved. The multiple time scale technique is applied to solve the nonlinear differential equations governing the system up to the second order approximation. All possible resonance cases are deduced at this approximation and some of them are confirmed by applying the Rung--Kutta method. The main attention is focused on the stability of the steady-state solution near the simultaneous principal resonance and the effects of different parameters on the steady-state response. A comparison is made with the available published work. [DOI: 10.1115/1.3085884] Keywords: rotor-active magnetic bearing, time-varying stiffness, multi-external excitations, stability, multiple-valued solutions, jump phenomenon

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.

This paper presents a new permanent-magnet (PM) brushless machine for wind power generation. This machine adopts an outer-rotor topology, aiming at capturing wind power directly. In order to achieve high power density, a high-speed PM brushless generator is artfully integrated with a coaxial magnetic gear. The design details, with emphasis on the special constraints of wind power generation, are elaborated. By using the time-stepping finite element method, the static characteristics as well as no-load and on-load operations are simulated. A prototype is also built for experimentation. Both simulation and experimental results are given to verify the validity of the proposed machine. Finally, a quantitative comparison is made to justify that the proposed machine is of smaller size, lighter weight, and lower cost than its counterparts. Index Terms--Finite-element method (FEM), magnetic gear, outer rotor, permanent-magnet (PM) machine, wind power generation.

The paper outlines methods developed to obtain circuit parameters of a superconducting synchronous generator with a coreless rotor. The need for full three-dmensional (3D) finite element modeling is emphasized and appropriate techniques devised to estimate relevant equivalent characteristics. The methods described use steady-state ac models, predominantly in the rotor frame of reference; the use of transient or full rotating machine models is avoided. Index Terms--Coreless rotor, equivalent circuit parameters, superconducting synchronous generator.

Bearingless induction motors have combined characteristics of an induction motor and magnetic bearings. Bearingless induction motors tend to suffer from the influence of rotor resistance variation under field-oriented control because magnetic suspension is sensitive to magnetic field rotational position error. In this paper, a novel rotor resistance identification technique based on variables in the magnetic suspension control loop is proposed. The rotor resistance is identified from suspension force command variations under static force generation by suspending an external shaft weight. Thus, a real-time on-line identification of the rotor resistance variation arising out of loading and temperature changes is possible with the regulation of magnetic field direction. Index Terms--Bearingless motor (BeLM), induction motor, magnetic suspension, rotor resistance identification.

Asymmetry in the magnetic circuit, around the air gap circumference, in a hydroelectric generator will give rise to a unbalanced magnetic pull. In this paper, a hydropower rotor system is modeled and the influence of electro-mechanical forces due to overexcitation is analyzed. The active power has been kept constant and the rotor excitation has been changed in order to vary the output of reactive power. The electromagnetic field is solved with the finite element method. Two electromagnetic models are compared: one with and one without damper winding. The mechanical model of the generator consists of a four degrees of freedom rigid disk connected to an elastic shaft supported by two bearings with linear properties. It has been found that the unbalanced magnetic pull slightly increases for reactive loads resulting in a decrease of natural frequencies and an increase of unbalance response. When the damper winding is included, the magnetic pull will decrease compared to the model without damper winding, and the pull force has two components: one radial and one tangential. The tangential component can influence the stability of the mechanical system for a range of design parameters. [DOI: 10.1115/1.2723822]

High rotation speed is the key to enhanced power density in rotating machines. High speed, shock, and construction considerations argue for solid rotors. However, output transient voltage requirements cause concern that changes in the field current will not be registered quickly in the stator. This paper examines different techniques for estimating the machine time constant, including an analytic solution of a smooth air gap machine and a transfer relation solution based on time harmonic solutions. It discusses an empirical solution and an equivalent surface current approach for predicting the loss in the rotor. These solutions compare favorably to rotational transient finite-element solutions. Index Terms--Harmonic, power dissipation, rotating machine, transfer relation, transient, wound rotor.

A superconducting motor consisting of high temperature superconducting (HTS) rotor, which has the rated power of 100 HP at 1800 rmp, and air-core stator is under development in Korea Electrotechnology Research Institute. The design, fabrication and test results of High Temperature superconducting (HTS) field coils are discussed.

The construction and test results of the High Temperature Superconducting (HTS) squirrel cage induction motor are presented. Test results indicate that the speeds of the HTS induction motor are the same with synchronous speed up to 2.6 Nm and 1788 rpm at 9.7 Nm.

Rotor eddy-current loss is usually significant in high-speed permanent magnet brushless dc (PM BLDC) motors. On the other hand, the rotor is usually protected with a nonmagnetic retaining sleeve. The influence of the conductivity of the retaining sleeve on the rotor eddy-current loss is analyzed in this paper. Furthermore, utility of a conductive copper shield between the sleeve and magnets is demonstrated. Although eddy current is induced in the copper shield, causing additional loss, its magnetic field can smooth the varying field in the rotor and reduce the overall eddy-current loss dramatically. The relationship between the thickness of copper shield and the rotor eddy-current loss is also examined. Index Terms--Conductive shield, high-speed motor, permanent magnet brushless dc (PM BLDC) motor, retaining sleeve, rotor eddycurrent loss, temperature rise.

The theoretical design of an aromatic hydrocarbon rotor made of pure hydrocarbons and driven by a circularly polarized electric field is presented. Very high electric fields are required to drive these motors due to the large moment of inertia.

The self-excitation of a switched reluctance (SR) generator via the drive-train dc link capacitance and compounded by the stored inertial energy of the connected mechanics is discussed. The potential for transient self-excitation of the SR generator via residual magnetization of the machine rotor is suggested and the SR generator system steady-state control is discussed.