Analysis And Control Of Internal Composite-Rotor Controllable-Flux PMSM

Vlado Ostovic brought forward the idea of internal composite-rotor PMSM—memory motor at first. But there are disadvantages in structure and mechanical behaviors. A new class of internal composite-rotor controllable-flux permanent magnet synchronous machine (PMSM) is proposed in this paper. The radial-set magnets are NdFeB with high remanent flux density and coercive force. The tangential-set magnets are AlNiCo with high remanent flux density and low coercive force. Applying a pulse of stator current id, the magnetizing intensity and direction of AlNiCo are controllable. The flux created by NdFeB is partially bypassed by AlNiCo in the rotor. So the air-gap flux is controllable, and the PMSM operates in wide speed.The internal magnetic field distribution in two extreme magnetized situations of the model PMSM was analyzed by finite element analysis. The proposed idea is proved viable. And the dimension of permanent magnet and magnetic structure are demonstrated. When the q-axis larger magnetic resistance and smaller inductance are designed, the result of weakening-flux will be better. Also the influence of armature reaction on the air-gap flux is weakened.On basis of characteristics of internal composite-rotor controllable-flux PMSM, double close loops of vector control system are designed with adopting SVPWM. Distinguishing with other vector control systems, control strategies of i=iq and id=0 are adopted to maintain the air-gap flux in condition of low speed and constant torque. When PMSM operates in high speed, make sure iq=0. And in a fraction of period of current, applying a pulse of id with controllable amplitude and direction in three-phase stator windings induces magnetomotive force of d-axis armature reaction. The AlNiCo intensity and direction of magnetization varies, and the air-gap flux is reduced. When the pulse of id disappeared, control strategies of i=iq and id=0 are still adopted. There is only a load current—q-axis current id in stator. Due to low copper loss, the motor economically operates in wide range. Simulation model of vector control system is built in Matlab/Simulink. The simulation results are analyzed, and the proposed assumption is proved viable. The vector control system of internal composite-rotor controllable-flux PMSM has good static and dynamic characteristics.