Research On Flux Weakening Control Of Permanent Magnet Synchronous Motor

In recent years,with the continuous development of permanent magnetic materials,improvement of power electronics technology and breakthroughs of AC machines,permanent magnet synchronous motor(PMSM)is being used more and more widely in areas such as aerospace,motorized spindle of CNC machine tool,high-speed railway and electric vehicle.With the more widely use of PMSM,there will be an increasing requirement for its performance.It not only needs to be able to output large torque at low speed,but also needs to operate at high speed with constant power.Because the flux linkage of rotor permanent magnet of PMSM is constant,it can no longer raise speed when the motor reaches the turning speed limited by inverter output voltage.At this time,it is necessary to adopt the flux weakening(FW)method to enlarge the speed range.For surface-mounted PMSM,it is harder to implement FW method because its d-axis and q-axis inductances are smaller than interior PMSM's.Therefore,it is necessary to do research of its FW method.In this paper,firstly,for surface-mounted PMSM,the leading angle FW and external voltage loop FW methods are studied based on the analysis of the principle of FW.And the SVPWM over modulation method is used to improve the utilization ratio of bus voltage of inverter.What's more,the notch filter is proposed to ameliorate the problem caused by the over modulation of the decease of the speed control ability in the FW region.Secondly,for the problem of cross coupling of d-axis and q-axis currents in high speed,a decoupling control method of current loop based on complex vector is proposed,which takes the control delay into consideration.And for the transient current oscillation caused by this method,a compensation method is proposed based on single d-axis virtual resistor.Finally,the proposed methods are simulated with Simulink and experiments are carried out with dSPACE using the proposed methods.Simulation and experiment results affirm the effectiveness and validity of the proposed methods.