Research On Design And Control Of Multiphase Double Stator Hybrid Permanent Magnet Motors

With the breakthrough of rare earth materials,the rare earth permanent magnet motors as a kind of important device for energy conversion,have become an important part of modern industry,transportation,aerospace and other fields.Their economy and reliability have always been research hotspots.The conventional rare-earth permanent magnet motors have the difficulty in speed expansion and suffer from the additional losses caused by field-weakening current.The hybrid permanent-magnet motors with both low-coercivity permanent-magnet poles and rare earth permanent-magnet make the flux linkage of permanent magnet motors changable.Therefore,it provides a new dimension in the field weakening for speed expansion and efficiency optimization of permanent-magnet motors,and thus has the advantages in application of variable-load scenarios.The low-voltage and high-power applications such as elevators and conveyor belts not only require high efficiency and reliability of the motor drive system,but also need a large current output capability.The combination of double-stator motor structure,fractional-slot multi-phase concentrated winding,and hybrid permanent-magnet excitation technologies is beneficial to meet the high-current,high-efficiency,and highreliability operation requirements of low-voltage high-power motor drive systems.In this paper,a 20-pole 24-slot double-stator hybrid permanent-magnet motor is designed.It is a fractional-slot concentrated winding hybrid permanent magnet motor with adjustable permanent-magnet flux linkage,and is designed from the comprehensive consideration of poleslot coordination,winding selection,and magnetic pole matching ratio.The torque ripple of the motor is improved by the topology,in which the axial double stator is staggered by 15° electrical angle in the circumferential direction.For this motor,a dual six-phase control model is studied.Essentially,a single stator is used as a basic unit,and a closed-loop current control method with a phase shift of 30° is used for dual three-phase windings in each stator.The two stators share a common closed-loop speed controller.The generation of inverter bus current is analyzed to solve the high-frequency current ripple of the DC-side bus caused by the superposition of bus-current peaks,when the dual-stator motor system uses multiple inverters in parallel.The corresponding relationship between the waveform and the switching pattern of the inverter is analyzed.By adjusting the switching state sequence within the switching cycle,it is possible to reduce the bus current ripple.On this basis,a coordinated modulation method is proposed for paralleled inverters,which can effectively reduce the high-frequency current ripple in the DC bus.To satisfy the requirement for online regulation of permanent-magnet flux linkage of hybrid permanent-magnet motor,the characteristics of flux linkage during magnetizing and demagnetizing processes of fractional-slot concentrated winding motor are studied by comparison of an 8-pole 48-slot integer-slot distributed-winding permanent-magnet motor.Based on the magnetic field harmonic decomposition of the 20-pole 24-slot motor and the parallelogram hysteresis model of the low coercivity(Al Ni Co)magnetic poles,it is revealed that different magnetic poles need to be magnetized or demagnetized at different optimal positions,when the flux linkage of the motor are adjusted.The magnetization model with five parts of the flux linkage and the multi-pulse magnetization method under are proposed,which can effectively reduce the extra copper consumption caused by the magnetization process.Based on the JMAG finite element software and Matlab/Simulink software,the finite element simulation model for the electromagnetic field analysis and the simulation model for the inverter control circuit have been built,respectively.The simulation has been carried out for the motor and control method.The experimental prototype of a 20-pole 24-slot double-stator dual-six-phase hybrid permanent-magnet motor and the drive inverter are developed.The working principle of the motor,the proposed cooperative control method and the optimized magnetization strategy are verified experimentally.