| Permanent magnet synchronous motor(PMSM)is widely used in industrial fields due to its advantages such as simple structure,small size,light weight,low loss and high efficiency.In the compressor,washing machine and other applications,the compressor’s compressing gas,washing machine’s dehydration and other conditions,the motor works in high-speed flux-weakening region.If the control is not appropriate,the system is easy to be unstable.In this paper,PMSM is taken as the research object,and the research is carried out from the aspects of flux parameter identification,out-of-control analysis and hybrid flux-weakening control strategy.The main research contents of this paper are as follows:Research on PMSM flux parameter identification.The control performance of PMSM largely depends on the accuracy of motor parameters,where to ensure identification accuracy existing flux identification method normally involves in complex mathematic calculation.In this paper,a flux identification method based on recursive least square method with discounting factor is proposed for reduction of computation load.This method adopts the fitting recursive least square method to identify flux linkage,which has small amount of calculation and only needs to save the previous estimation value during the operation with small storage space.Aiming at solving the problem of"data saturation"in least square method,forgetting factor is introduced to enhance the proportion of current data in estimation and a discounting method is proposed to to reduce the influence of the noise of flux identification caused by forgetting factor.The method has the advantages of higher precision and faster response to time-varying signals.Research on out-of-control analysis of PMSM flux-weakening operating region with solution of switching point.In order to further widening operating speed range of PMSM in constant power flux-weakening operating region,it is necessary to switch the control mode to make it work in the deep flux-weakening operating region.Consequently,accuracy of mode switching time would directly affect the control stability.In this paper,based on the qualitative analysis of the existing conditions of deep flux-weakening operating region of PMSM,flux-weakening operating regions and the reasons for the instability of switching from constant power flux-weakening control to deep flux-weakening control,the current,speed and power at the switching point are derived theoretically and the accurate calculation formula of the speed of the switching point is obtained as well,which can provide a reference for switching from constant power flux-weakening operating region to deep flux-weakening operating region.Finally,the simulation is carried out from the electrical constraint diagram and power point,and the speed of the switching point is determined according to the switching point current,which verifies the validity of the theoretical analysis and calculation of the switching point.Research on PMSM flux-weakening control strategy.For PMSM in the flux-weakening operating region,the curves of MTPA and MTPV are analyzed based on the optimal current trajectory,and the constraint conditions of constant torque operating region,constant power flux-weakening operating region and deep flux-weakening operating region satisfying the optimal current trajectory are solved.The constraint conditions could be used as the basis of current reference instruction.The negative i_dcompensation method,lead angle method and gradient descent method are analyzed and compared.Based on the comprehensive consideration of the consistency of d,q-axis current control and the complexity of the control algorithm of flux-weakening operating region,a hybrid flux-weakening control strategy based on lead angle combined with gradient descent method is proposed,which realizes the simultaneous d,q-axis current control and the control algorithm is simple.According to the research content of this paper,the PMSM system simulation model and hardware-in-the-loop experimental platform are built,and the simulation and experimental research are carried out to verify the correctness of theoretical analysis and control strategy. |
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