Analysis On The Trajectory Oscillation Of Permanent Magnet Spherical Motor And Its Vector Control Strategy

Permanent magnet spherical motor(PMSM) is a new typical electromagnetic actuator, whose rotor can realize 3 degrees of freedom(3-DOF) movement. Since it has wide application prospects in areas like panoramic camera, robot joints, artificial eyes and satellite attitude control, PMSM has become a hot research point both domestic and overseas. Compared with conventional rotary machines, many theoretical problems for PMSM are still in exploratory stage. This paper aims to provide reference for the design and control of 3-DOF motors.First, based on the theory of synchronous rotating magnetic field, a reference current equation is proposed, and an excited rotary/tilted magnetic field in space is proved via finite element analysis, least square method, and spherical harmonic theory. The spatial phase of the main harmonic component is shown to link directly with the current phase angle and amplitude ratio. The stator magnetic field can rotate and simultaneously its rotation plane can be tilted. From the perspective of gyro mechanics, the possible trajectory oscillation that may occur when a spinning rotor is tilted under this reference current equation is discussed.To prevent the above-mentioned trajectory oscillation, the control strategy is improved. Based on the principle of equivalent PM and spherical harmonic theory, this paper derived the direct mapping relationship between the harmonic component of the stator magnetic field and excitation current. Again, according to the spherical harmonic analysis on the rotor magnetic field, a local mechanical d-q-p coordinate, which is fixedly connected with the rotor and its corresponding electrical D-Q-P coordinate are established. Further, by using coordinate and vector transformation, as well as the electromagnetic power relation, an airgap flux-oriented M-T coordinate system is established, under which the electromagnetic torque is decoupled. The 3-dimensional vector decoupling control of PMSM is achieved.To obtain a better oscillation suppression effect, the stator windings are then reconfigured into a dual-redundancy design. A dual-vector complementary control strategy is proposed. Simulation research is carried out under Simulink environment. Results show that the proposed control strategy can realize the continuous path control of the rotor’s output shaft spinning at a constant speed with a good accuracy. which lays a foundation for the subsequent experiment on the prototype machine and research on other similar devices.