Design of open-loop controller for permanent magnet spherical motor

This paper presents an open-loop control system design for a permanent magnet spherical motor (PMSM). The proposed spherical motor consists of a ball-shaped rotor with a full circle of 8 permanent magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential 24 air-core coils. Based on the torque model of the PMSM, the relationship between current input and torque output can be demonstrated. We design the open-loop controller by decoupling the spinning motion control, which is based on the torque equilibrium theory, from the inclination motion control. Two types of spinning motion control models are proposed and analyzed. The open-loop controller can make the PMSM have the ability to spin continuously and tilt to certain angle. The experiment of open-loop control system based on a personal computer and current controller is designed to validate the control method at last.