Torque Superposition Compensation Fault-tolerant Control For Dual Three-phase Pmsm With An Inverter Single-leg Open-circuit Fault

Dual three-phase permanent-magnet synchronous motors(DTPMSM)have wide applications in electric vehicles due to advantages such as excellent control performance and outstanding fault tolerance capability.However,in some operating conditions such as driving electric trucks,which requires longtime high load operation,the electrical fault is liable to occur in the DTPMSM or its control system,including inverter single-leg open-circuit fault.When inverter single-leg open-circuit fault occurs,motor operation will be unstable and may result in secondary fault and thus greater risk.Therefore,it is necessary to design a fault-tolerant control strategy for the DTPMSM control system under the inverter single-leg open-circuit fault to ensure the stable operation of the motor.In this thesis,the mathematical model of the DTPMSM and its control strategy,and the mathematical model of the DTPMSM after the electrical failure and its fault-tolerant control strategy are investigated.Firstly,the basic mathematical model of the DTPMSM in the natural coordinate system is derived based on the spatial position structure of each winding of the DTPMSM and the electromagnetic theory.Since the model is a seventh-order and strongly coupled system,a reduced-order and decoupling model of the DTPMSM is derived based on the double d-q transform and the vector space decomposition(VSD)transform,respectively,to facilitate the understanding and analysis of the DTPMSM.Then the control system of the DTPMSM is derived based on these transforms.The equivalence of the models under the two transforms is certified by theoretical analysis and simulation.So,the VSD transform,which better reflects the multi-degree of freedom control of the DTPMSM,is chosen for modeling in the following.Secondly,inverter single-leg open-circuit fault is equated to the DTPMSM one-phase winding open-circuit fault when modeling.Then the post-fault DTPMSM model is constructed.And the minimum stator copper losses control and the maximum torque-production capability control of the post-fault DTPMSM are derived by changing the VSD transform matrix and z-axis setting.The conventional fault-tolerant space vector pulse width modulation(SVPWM)strategy,which can continue to utilize each phase winding of the post-fault DTPMSM,is also derived by getting the phase winding originally connected to the faulty inverter leg to link to the DC-link mid-point.The effect of the inverter single-leg open-circuit fault is analyzed by simulation.And the effectiveness of these fault-tolerant control strategies is verified by simulation.Finally,since the present fault-tolerant control strategies under inverter single-leg open-circuit fault cannot make full use of each phase winding of the DTPMSM,which limits the torque-production capability.This thesis proposes a torque superposition compensation(TSC)control which can minimize the stator copper losses while increasing the torque-production capability.Based on the fault-tolerant measure of getting the phase winding originally connected to the faulty inverter leg to link to the DC-link mid-point,the model of the DTPMSM is reconstructed as the combination of the symmetric dual three-phase windings torque model and the asymmetric five-phase windings compensation torque model for U_d/2 voltage level according to the torque superposition.Then the post-fault VSD transformation matrix is derived for fault-tolerant control.And the decoupling model in the d-q subplane is constructed for the coupling in the d-q subplane of the post-fault motor to suppress the output torque pulsation and the speed pulsation.The effectiveness of the proposed TSC fault-tolerant control strategy and the decoupling model in the d-q subplane are verified by simulation,respectively.