Permanent Magnet Excitation Research Articles

Self-starting permanent-magnet a.c. motors

Many of the earliest dynamo-electric machines had permanent-magnet excitation. Gradually, however, this form of excitation was replaced by excitation from electromagnets, which seemed to offer the advantage of stronger magnetic fields and so more power from a total volume of material. Since then, many signs have appeared that indicate a reversal of this trend. Small permanent-magnet direct-current motors are commonplace in automobiles. Perhaps most interestingly, new forms of alternating-current machine using permanent magnets have begun to appear, and these show some interesting advantages compared with alternative drive systems. The self-starting permanent-magnet synchronous motor is essentially a new form of motor with a wide variety of applications

Hybrid permanent-magnet synchronous motors

The paper provides a comprehensive review of the development of self-starting synchronous motors with permanent-magnet excitation. Several new configurations of machine are described and their performance is demonstrated. Some important aspects of the performance are discussed. It is shown that the finite-element method of computing permanent-magnet fields, discussed in an earlier paper, gives an accurate prediction of performance.

Linear scalar-potential models for permanent-magnet circuits

A scalar-potential equivalent network is developed to represent permanent magnets with linear operating characteristics and their surrounding air regions. The method of allowing for the effect of current in the scalar-potential formulation is explained and demonstrated. The use of the technique is illustrated by means of examples. In the first, the calculation of the leakage factor in a permanent-magnet circuit with an airgap is examined. The influence of magnet permeability on leakage factor and the limitations of a more traditional technique are explained. In the second example, the method for calculating demagnetisation limits is demonstrated for electrical machines with permanent-magnet excitation adjacent to the airgap. The method is applied to the calculation of field flux-density distributions set up by two permanent-magnet rotors, and the results compared with distributions obtained experimentally. Finally, the general ‘dynamic’ problem is considered. When reduced to its most basic form, the network is shown to model static and dynamic magnet behaviour in a manner similar to other techniques which assume point operation within the permanent magnet.

DC motor with electronic commutation, permanent magnet excitation, and galvanomagnetic signal transmitter

DC motor with electronic commutation, permanent magnet excitation, and galvanomagnetic signal transmitter

Application of Modern Permanent-Magnet Materials to the Excitation of a Slow-Speed Power Servomotor

The main requirements of low-speed, dc power servomotors used as drive members of director control systems are for fast speed of response coupled with optimization of size and weight for a given torque output. It can be shown that the over-all time constant of such a dc machine is inversely proportional to the gap density squared; thus, where physical size and temperature rise of the field windings are important design limitations, the use of modern, high-energy permanent-magnet materials becomes advantageous. This paper describes the conversion of a conventional 6-pole, 1-hp, 100-rpm machine to one having permanent magnet excitation employing Columax (Alnico VB, DG) poles. Difficulties associated with machining, and magnetizing and demagnetizing the 6-pole stator in situ are discussed, and a study of the maximum demagnetization forces existing in such a machine, carried out with the aid of Hall plates, is given. A comparison of both the dynamic and the steady-state performance of the conventional machine and the permanent magnet machine, shows the feasibility of using modern permanent magnet materials for such an application.

Induction motors with permanent magnet excitation

INDUCTION MOTORS have been built in Germany with a free running member carrying d-c excitation. They had excellent characteristics, including 100% power factor. Permanent magnets have been substituted for d-c excited poles in magnetos and in synchronous motors with good results. Why not, one may ask, substitute them for the d-c free running member of the German motor? Assuming this could be done, a design for an 8-pole 10-hp 60-cycle motor, based on the German motor, was made, its equivalent circuit analyzed, and its performance computed.

Characteristics of Induction Motors with Permanent-Magnet Excitation

Characteristics of Induction Motors with Permanent-Magnet Excitation

Design Principles of Flux-Switch Alternators [includes discussion

The general problem of the design of a peak-power minimum-volume high-frequency alternator which employs the flux-switch principle is discussed. Included in this paper are analyses of general configuration, generated voltage and frequency, magnetic circuit, generator losses, and materials. A design procedure which employs the use of a set of empirically derived constants which determine various mechanical and electrical parameters is presented. The design charts can be used for flux-switch alternators ranging in power from 100 to 5,000 watts and for shaft speeds from 10,000 to 50,000 rpm. A sample design based on the use of the design charts is developed for a 50,000-rpm 3-kw 250-volt single-phase flux-switch alternator with permanent magnet excitation.