Research On Interior Composite-Rotor Controllable-Flux Permanent Magnet Synchronous Machine

In this dissertation,diverse field-weakening methods are researched and analyzed in detail.Based on the deficiencies of composite-rotor controllable-flux PMSMs with sandwich structure proposed by Vlado Ostovic,three types of magnetic circuit structure of interior composite-rotor controllable-flux with different poles are proposed.Two kinds of PMs,NdFeB and AlNiCo,are fully used in the new structure motor.Their features,that NbFeB PM has high remanent flux density B_r as well as high coercive force H_c,and AlNiCo PM has high B_r but low H_c,are especially taken into account.These PMs are fitly placed in the rotor spaces,and their sizes are decided appropriately to make them work well together.With the proposed structure,the speed of PMSMs can be controlled by a field-weakening regime in significantly wide range without losing any basic performance of the motor.In the operating mode,if the controllable direct axis current vector pulses on stator windings are changed by the speed regulation driving system with close-loop structure,the magnetization direction and the retentiveness intensity of AlNiCo PMs are changed consequently.As the magnetization directions of both PMs are uniform,AlNiCo PMs will push the magnetic flux of NdFeB PMs to stator side,and the air-gap magnetic flux becomes strongest although AlNiCo PMs contributes little to it.As the magnetization directions of PMs are opposite,the air-gap magnetic flux is weakened because part flux of NdFeB PMs is bypassed by AlNiCo PMs.The proposed motor structures are named memory motors for their ability to preserve the controllable flux in rotor magnets.A static magnetic circuit device was designed to simulate the mechanism of controllable-flux PMSM.Related experiments revealed the principle of the interior composite-rotor controllable-flux PMSM.Consequently,the law of two kinds of PMs' action spot change during and after magnetization were cognized in the process of controlling rotor-flux.For more awareness and understanding of the magnetization,the equivalent magnetic circuits of different action spots were present. Finite-element method was adopted to analyze and calculate the magnetic field of 3 kinds of interior composite-rotor controllable-flux PMSM,and the internal magnetic field distribution and air-gap magnetic field waveforms in different work conditions are shown, and the impact on the d-axis PM-flux created by load current was analyzed.The increment of q-axis magnetic reluctance in interior composite-rotor controllable-flux PMSM can not only reduce the q-axis induction,decrease the quadrature axis inductive drop,raise the utilization ratio of input voltage from inverter,but also reduce the impact of q-axis armature-reaction magneto-motive potential generated by load current on d-axis PM flux, expend PM-flux weakening range and speed scope.The general principle of the rotor PM size selection was given.Reasonable choosing the NdFeB PM width make the NdFeB PMs contribute to PMs main air-gap flux as much as possible.In order to avoid the extreme cases that the NdFeB PMs is irreversibly degaussed by the demagnetizing magnetomotive force generated by the stator windings armature reaction,the NdFeB PM thickness should be decided reasonably.In addition,the cost of NdFeB PM,the utilization ratio of material and the processing technology also should be taken into account.By selecting AlNiCo PM reasonable width,the size of the controllable flux can be effectively adjusted,and then the field-weakening multiples are regulated.For example,when the AlNiCo PM length is equal to 0.5～0.7 times of NdFeB length,the field-weakening multiples can reach more than three times.Selecting magnetization direction length of AlNiCo PMs could follow two principles.One is that after the AlNiCo and NdFeB magnetized by the i_d pulse,the AlNiCo must not be demagnetized or remagnetized reversely by the NdFeB;the other one is that the total magnetomotive force source of AlNiCo is higher from 20%to 30%than the magnetomotive force for the external magnetic circuit.As an example,electromagnetic computing program for 4-pole interior composite-rotor controllable-flux PMSM was developed and a prototype was made.The experimental results coincide with expectation.