| The air gap magnetic field of the hybrid excited synchronous machines(HESMs)is formed by the magnetic field generated by the permanent magnet and the excitation magnetic field generated by the dc field winding.Compared with the traditional permanent magnet machines,HESMs can not only maintain the advantages of permanent magnet synchronous machines,such as high power density,high torque density and high efficiency,but also the adjustment of magnetic flux is more flexibility by changing the field excitation.Thus,higher efficiency at the low speed region and in a wider operation area can be obtained.This is much helpful for electric vehicles with variable speed requirements,so it has a good application prospect.The research in this thesis is based on a 12-slot,10-pole hybrid excited switched flux permanent magnet(HESFPM)machine.This thesis proposes two optimization control methods for compensating the flux weakening current in the high-speed region,so as to improve the flux weakening performance of the HESFPM machine.The details include the following contents:Firstly,the topology structure,operation principle and mathematical model of the HESFPM machine in the rotating coordinate system are given.Based on the mathematical model,the research on the flux weakening theory of HESFPM machine is carried out.The factors that affect the change of machine parameters are analyzed.Combined with the voltage limit ellipse,the influence of machine parameters on output performance is analyzed,and a basic current distribution compensation control method considering the armature winding voltage drop and the inductance nonlinearity is proposed.The simulation control model was built on the Simulink platform,and the changes of output performance before and after compensation were compared and analyzed.Secondly,in order to reduce the dependence on the machine parameters,the flux weakening method is optimized and the flux weakening control method based on current compensation is proposed in this thesis.This method uses the difference between the phase voltage fed back from the HESFPM machine and the maximum output voltage of the inverter to divide the operation area into a low speed area and a high speed area.In the low speed region,a control algorithm of the maximum torque per armature current ratio is used.In the high-speed region,the difference between the machine phase voltage and the inverter’s maximum output voltage is adjusted by PI as the compensation amount of the d-axis current(or dc field current)to modify the reference current.When the d-axis current(or dc field current)reaches the minimum value,the machine is further weakened by the dc field current(or d-axis current),and the difference between the d-axis current(or dc field current)before and after the limitation is used as the compensation amount of dc field current(or d-axis current).The proposed method and the basic current distribution method are compared and verified by simulation experiments results.It can be seen that with the control strategy proposed in this thesis,the overshoot is smaller and the speed of entering the steady state is faster.Finally,a prototype experimental platform based on Micro Lab Box and MATLAB/Simulink was built,and the flux weakening control strategy based on current compensation proposed in this paper was experimentally verified.The results show that when the phase voltage of the HESFPM machine changes,the control system can judge the region in which the machine operates and give the reference current in this region.The machine’s armature current and dc field current can quickly follow the given value of the control strategy.The experiment proves the feasibility of the control strategy. |
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