Optimal design of a Halbach magnetized permanent magnet motor applied in electrical marine propulsion system

Abstract

Electrical marine propulsion system has many advantages over traditional diesel drive system, as it offers large r torque capability with lower noise and vibration, therefore it is a promising candidate in the future trend. Permanent magnet (PM) brushless ac motors employing Halbach magnetized rotors provide attractive merits such as high power density, high acceleration feature and low cogging torque, which are suitable for the marine application. This paper is to design and optimize a Halbach magnetized permanent magnet motor applied in electrical marine propulsion system. With the employment of finite element analysis (FEA), the split ratio, PM thickness and slot opening are optimized to achieve a maximal torque output and a relatively small torque ripple. Moreover, the unequal height magnet poles are employed and analyzed in order to improve the torque capabilities, and then meet the specific design requirements in the marine propulsion system. Power propulsion system o f warship has emerged for over 100 years, and it has been developing rapidly with the global exploration to ocean. Electrical marine propulsion system, which is a hot research area in ship manufacturing industry, gains many advantages over traditional diesel drive system, as it is mo re efficient, clean and energy-saving with lower noise and vibration, therefore it is a promising candidate in the future trend. The essential part of the system i.e. the electric propulsion motor which has large torque density, smalle vibration and highe reliability is demanded to meet the rapid marine propelling development (1). Co mpared with traditional permanent magnet (PM) strcture motors, Halbach magnetized PM brushless ac machines offer a number of attractive features, wh ich are suitable for ship propulsion: