Control Strategy Of Novel Multi-degree-of-freedom Spherical Induction Motor

As a special induction motor,the novel multi-degree-of-freedom(multi-DOF)spherical induction motor(SIM)has the advantages of high integration,simple mechanical structure and no fixed pole of rotor.It is expected to be used as hub motor instead of traditional wheel and steering system to drive the vehicle forward,backward and steering directly.It can provide a reference for the realization of vehicle omnidirectional steering function while realizing the optimized layout of the whole vehicle,which is significant to the development of urban smart transportation in the future.At present,the design ideas and methods of the motor have been systematically discussed,but the research on motor drive control is less involved.Therefore,dependent on the design principle and structural characteristics of multi-DOF SIM,the control strategy of this motor is investigated in this paper.Firstly,the design scheme of multi-DOF SIM was briefly analyzed.According to the design theory of linear induction motor(LIM),these parameters of equivalent LIM were determined.And the finite element model of multi-DOF SIM was established by arc and spherical processing.The electromagnetic simulation analysis was carried out utilizing Ansoft Maxwell,and the results of magnetic field transient solution preliminarily verified the correctness of structural parameters.Secondly,the mechanism of dynamic end effect caused by the stator with finite length was analyzed,and its influence was calculated equivalently.Combining with the idea of vector transformation,the transient equivalent circuit and equations of SIM with single stator considering dynamic end effect were established in synchronous coordinate system.And the mathematical modeling and simulation analysis were proposed by Matlab / Simulink.To test the accuracy of the mathematical model,the respective output characteristics of mathematical model and electromagnetic simulation were compared and analyzed.For the multi-DOF drive of the motor,a segmented control strategy was proposed.Four working sections were set,the working state of stators was adjusted according to the deflection angle of the spherical rotor.And the roles of stators on the spherical rotor were combined to achieve the oriented control of rotor.As for the drive scheme of the rotor,vector control system(FOC)and direct torque control(DTC)system were designed respectively.By combining the two systems with segmented control system respectively,the multi-DOF driving system based on FOC and the multi-DOF drive control system based on DTC were constructed.Simulation results of mathematical model indicate that above two driving schemes can realize the driving control of spherical rotor with two rotational DOF without the limitation of rotor deflection angle.Finally,in order to systematically verify the rationality of motor design and control strategy,the finite element model of SIM with single stator in Maxwell 2D was coupled with the DTC system in Simulink by utilizing the field circuit coupling characteristics of Simplorer.And a joint simulation platform of multiple physical fields was established.In addition,SVPWM technology was introduced and a speed controller based on sliding mode variable structure was designed to improve the control performance of DTC system.