Research On Torque Fluctuation Suppression For Dual Three-phase Permanent Magnet Synchronous Motor With Short-circuit Fault

The development of electric vehicles,which are both energy-efficient and environmentally friendly,can reduce the use of traditional fuel vehicles,thus effectively alleviating environmental pollution and the energy crisis.The drive system of an electric vehicle should have the ability to run reliably and smoothly over a long time.The use of dual three phase permanent magnet synchronous motors(DTP-PMSM)in the drive system of electric vehicles has obvious advantages over traditional three-phase motors in terms of control performance and fault tolerance after a fault.When a short-circuit fault occurs in a drive motor,the current in the winding will increase dramatically,causing severe local heating and spreading the fault,threatening driving safety.Therefore,it is of great importance to conduct an in-depth study of fault-tolerant control strategies after a short-circuit fault,so that the motor can still output a smooth electromagnetic torque after the fault.This thesis analyses and investigates the mathematical modeling,vector modulation algorithms and fault-tolerant control of short-circuit faults in DTP-PMSM.Firstly,the basic structure of the winding of DTP-PMSM is introduced and the advantages and disadvantages of the two common topologies,neutral point-isolated and neutral pointconnected,are analyzed.The mathematical model of DTP-PMSM is derived,and the decoupling mathematical model is constructed from the dual d-q coordinate transformation and the vector space decoupling(VSD)respectively,and the inner connection between the two coordinate transformations is analyzed.The basic principles of space vector pulse width modulation(SVPWM)are analyzed,in which the four-vector SVPWM can effectively suppress the harmonic losses generated in the harmonic subspace,and simulation models are built and analyzed.Secondly,the effect of short-circuit current on the air-gap magnetic field and torque is analyzed,and a stable torque can be output by reconfiguring the current in the non-faulty phase winding to compensate for the lack of torque due to the absence of normal current and suppress the torque pulsation caused by the short-circuit current.Based on the principle of constant magnetic motive force(MMF),a vector space decoupling transformation is used to derive a decoupling mathematical model of reduced order after removal of the faulty phase,which can effectively compensate for the torque loss and torque pulsation caused by the absence of normal current in the faulty phase.Finally,the compensation current coefficients are designed according to the effect of the short-circuit current on the rotational MMF of the motor,and the torque pulsation is suppressed by injecting compensation current into the remaining phase.At this point,the torque loss due to the absence of the short-circuit winding is compensated and the torque pulsation caused by the shortcircuit current is effectively suppressed.The performance of the topologies with neutral pointisolated mode and neutral point-connected mode are both investigated and compared.The effectiveness of the short-circuit fault tolerant control strategy for DTP-PMSM is verified by simulation.