Study On The Electromagnetic Loss Of Permanent Magnet Generator For Ships

With the development of shipbuilding and marine engineering, thescale and capacity of ship power system is improving continually, as thepower source of ships, the capacity of single generator for ships isbecoming larger and larger. Permanent magnet generator has uniqueadvantages on being used on ships, since it has many advantages such assmall size, high power density, high efficiency, etc. Especially the countryis now promoting the application of energy efficient motors, thedevelopment and application of permanent motors has a broad prospect.Generators for ships works in an harsh environment, theelectromagnetic loss of per unit volume increases synchronously with theincrease of power density, especially for high power density permanentmagnet motor, and small size results in heat dissipation difficulty due tothe humid and hot environment on the ship, which may results in thethermal demagnetization of permanent magnets because of hightemperature. Thus, it is important to calculate the electromagnetic lossprecisely, to reduce the electromagnetic loss by optimization design of themotor structure, so as to reduce heat source in the motor. In the way, theproblem of high temperature rise in the motor can be solved radically,reliable operation and energy efficiency of the generator can be realized.In order to study electromagnetic loss of high power densitypermanent magnet generators for ships, the main works in the paper are asfollows.Firstly, the paper summarized the calculation methods of rotor eddycurrent loss and stator core loss of permanent magnet motor studied bydomestic and foreign scholars. Electromagnetic numerical model of a prototype is established based on finite element method.Secondly, as the rotor eddy current loss of permanent magnet motoris mainly caused by harmonic magnetic field, which is constituted of thetime harmonics of winding currents and the space harmonics which iscaused by the uneven gap permeability. The gap permeability variesmainly because of the stator slots. The paper studied the influence of thechange of slot parameters on the electromagnetic loss of permanentmagnet motor, include the slot type, the slot opening width, the slotopening height, and the magnetic slot wedge permeability. And analyzewhen these parameters changes, its influence on harmonic magnetic fieldand electromagnetic loss of each section.Then, the effect of different structures of the rotor on theelectromagnetic field and electromagnetic losses is studied, includingdifferent magnetic structure, placement of the permanent magnet, thematerial and thickness of the sheath. Through comparative analysis, thepaper studied the electromagnetic field distribution and theelectromagnetic loss with different structure of rotor.Finally, a prototype is made, as it’s difficult to measure theelectromagnetic loss of each section directly in experiment, the paperintroduced a method for indirect measurement, in this way, theelectromagnetic loss of each section can be separated from the total loss.And the results were compared with the calculated results, thus verifiedthe accuracy of the calculation model used in this paper.