طراحی بهینه موتور BLDC مگنت دائمی نصب شده سطحی جهت برنامه کاربردی فضاپیما

ABSTRACT Optimal design of a surface mounted permanent-magnet BLDC motor for spacecraft applications

The BLDC motors have been proven to be the best all around type of motors for aerospace applications because of their long life, high torque, high efficiency, and low heat dissipation [1]. The torque produced in a Slotted PMBLDC motor can be classified as alignment torque (i.e., useful torque) and cogging torque. The alignment torque is produced due to the interaction of the PM with the stator conductors and the cogging Torque is caused by the variation of the magnetic energy stored in the air gap, due to the PM flux with the angular position of the rotor. Simply it is due to the interaction between the rotor magnetic flux and the variation of stator [2].

For high performance applications, torque smoothness is essential. Hence, it is very important to consider torque ripple minimization and its related harmonics without affecting the developed torque of the machine. The cogging torque is one of the disadvantages faced in the slotted motor design, as it causes high ripple in the torque generated by the motor.

The Attitude Control Systems (ACS) for future spacecraft applications requires an ideal choice of motor that has high torque density, zero cogging torque, high positional stability, high torque to inertia ratio and zero magnetic stiction. Stepper motors, a special case of BLDC motors cannot be used for critical ACS applications because of its high ripple torque.

Moreover the research work carried out by the authors [3] clearly reveals the magnitude of the detent torque present in the stepper motor which is almost 13 % of the developed torque. A slotless BLDC motor design however eliminates the tooth ripple component of cogging as well as has little slot harmonic effects thereby facilitating the need of smooth torque output required for the application. A slotless machine, however suffers from a generally lower magnetic flux crossing the motor air gap which results in a lower power output in the slotless design compared to an equivalent slotted design [4-5].

This reduction in the magnetic flux crossing the air-gap is compensated by the use of Halbach magnetized array having strong and uniform magnetic field. As per the requirements of the spacecraft application the outer diameter and axial length of the machine is selected as 104 mm and 40 mm respectively. Hence a design is to be developed in accordance with the specifications for spacecraft applications.