A superconducting homopolar motor and generator—new approaches

Abstract

Homopolar machines were the first continuously running electromechanical converters ever demonstrated but engineering challenges and the rapid development of AC technology prevented wider commercialisation. Recent developments in superconducting, cryogenic and sliding contact technology together with new areas of application have led to a renewed interest in homopolar machines. Some of the advantages of these machines are ripple free constant torque, pure DC operation, high power-to-weight ratio and that rotating magnets or coils are not required. In this paper we present our unique approach to high power and high torque homopolar electromagnetic turbines using specially designed high field superconducting magnets and liquid metal current collectors. The unique arrangement of the superconducting coils delivers a high static drive field as well as effective shielding for the field critical sliding contacts. The novel use of additional shielding coils reduces weight and stray field of the system. Liquid metal current collectors deliver a low resistance, stable and low maintenance sliding contact by using a thin liquid metal layer that fills a circular channel formed by the moving edge of a rotor and surrounded by a conforming stationary channel of the stator. Both technologies are critical to constructing high performance machines. Homopolar machines are pure DC devices that utilise only DC electric and magnetic fields and have no AC losses in the coils or the supporting structure. Guina Energy Technologies has developed, built and tested different motor and generator concepts over the last few years and has combined its experience to develop a new generation of homopolar electromagnetic turbines. This paper summarises the development process, general design parameters and first test results of our high temperature superconducting test motor.

Modeling the dynamics of a unipolar generator

“…Figure 11 shows the dependence of the angular speed of rotation of the rotor ω on time t for different values of the parameter R of the dynamic system described by equations. (7). It can be seen from this figure that the phase trajectories corresponding to the values R=1, 2, 3 have rest points…”

“…Various schemes and designs of unipolar generators are known [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. These include: Faraday disk, Tesla unipolar generator, models of Das Gupta, Forbes, Thury, Leroux, unipolar generators with T-shaped and bell-shaped rotors, N-machine of Bruce de Palm, unipolar machines of Neggerat, Poirson, Somed, Ugrimov, Pulain, Lifshitz, Mende, and others.…”

Bidirectional Tracking Robust Controls for a DC/DC Buck Converter‐DC Motor System

“…Where the driving of new classes of motors has been possible thanks to the power electronics [2]. Likewise, the use of the control engineering and power electronics [3], among other areas, glimpses the possibility of achieving a driving more efficient of the new forms of electrical energy generation [4].…”

Superconducting Super Motor and Generator

“…Perhaps the greatest advancements to date have been in the area of low rotation speed ship propulsion motors, where a power-to-weight ratio of about 0.5 kW/kg has been reported with a rotor wound from high temperature superconductor. This is an improvement by a factor of about five compared to a conventional motor, even though conventional copper air-core windings were employed on the stator, and a cryogenic cooling system, based on gaseous helium, is required [2], while several new designs and approaches are currently in progress [3,4,5].…”