Six Steps Commutation Torque and Dynamic Characteristics of Spherical Brushless Direct Current Motor

Abstract

This paper presents developing a new three-degrees of freedom (DOF) electromagnetic actuator referred to here as a spherical brushless direct current (SBLDC) motor. The SBLDC motor consists of permanent magnets (PMs) in a rotor and three layers of electromagnets (EMs) in a stator. The EMs in the middle layer of the stator generate a spinning torque, and the other two layers, placed symmetrically with respect to the middle, produce a tilting torque. Winding layouts of the EMs in each layer are analytically studied for decoupling between spinning and tilting torque. Furthermore, a six steps commutation is proposed to independently control the tilting torque as well as the spinning torque. The commutation torque model is validated by the moment method based distributed multipoles (MMDMP) according to various tilting angles and directions. Then, the commutation torque model is further utilized to develop open-loop control and analyze stability with respect to equilibria. Finally, the performance of the SBLDC motor and control system is verified experimentally using commercial brushless direct current motor (BLDC) drivers. The results show the substantial potential of the SBLDC motor in automation and mobility applications requiring orientation control with high-speed spinning.