Research On High Power Density Driving Method Of Hidden Permanent Magnet Motor

Multi electric and all electric aircraft based on electric propulsion technology plays an increasingly important role in aerospace and other fields.As the core component of electric propulsion system,brushless permanent magnet motor with hidden pole has the advantages of simple structure and high power density.However,the power density of traditional sine wave and square wave driving methods is controversial.In addition,the copper consumption and internal power angle produced by the motor during operation will reduce the output power of the motor.Aiming at the above problems,this paper studies the driving method to improve the power density of brushless permanent magnet motor.In the comparative test of sine wave and square wave control,it is found that when the output power is the same,the internal power angle of sine wave control method is larger,but the bus current is smaller,and the difference is more obvious with the increase of output power.Based on this phenomenon,this paper makes a theoretical analysis of the relationship between the harmonic content of the phase current and the back EMF of the two control methods and the output power,and finds that the fundamental component in the sinusoidal phase current can make better use of the higher harmonics in the back EMF,and the power density is higher.Finally,a simulation model is built to verify the conclusions.However,the square wave and sine wave driving methods have the problems of large copper consumption and large torque ripple respectively.In view of the shortcomings of the two driving methods,this paper plans and controls the phase current,and studies a driving method to reduce the copper consumption of square wave control.Compared with square wave driving method,this method can effectively reduce the influence of phase current discontinuity on power density,and the planned current 5th and 7th harmonic content is relatively low,which is conducive to improving power density.Compared with the sine wave drive method,the torque ripple and noise are reduced.Finally,the simulation shows that this driving method can effectively reduce copper consumption and optimize the problem of large torque ripple of sine wave driving method.However,the motor is a resistive load,which will make the phase current lag behind the back EMF at high speed.To solve the lag problem,the real-time lead angle control method is used to reduce the phase angle difference between the phase current and the back EMF.Based on the analysis of phase lag principle and compensation method,the control principle of lead angle is derived,and a real-time lead angle control method is proposed,which is improved on the basis of copper consumption minimum current drive method.This method can compensate the angle that the phase current lags behind the back EMF according to the speed,inductance and back EMF parameters,reduce the internal power angle under the minimum copper consumption driving method,and further improve the power density.