Research On Fault-tolerant Control Strategies Of The Dual Three-phase PMSM

Multi-phase permanent magnet synchronous motors(PMSM)are widely used in all kinds of energy,industry and production fields with the needs of energy conversion and control drives.They have the advantages of high efficiency,high power density and excellent fault tolerance,which makes them have a broad application prospect in the future.Due to the characteristics of multi-phase PMSM which include various phases and large degrees of freedom,more and more attention has been paid to the development of its ability of continuous operation under the condition of single-phase or multi-phase open-circuit fault.Besides,the fault-tolerant control strategy has gradually become the research hotspot.However,strategies for full use of the phases of the multi-phase PMSM to maintain the system operation in the most extreme open-circuit fault remain to be studied.In this paper,a fault-tolerant control strategy is proposed,which can keep the motor running in the open-circuit fault in any number of phases within four phases and in any positions.With the structure and principle of the motor allowing,aiming at the serious open circuit fault,the fault tolerance ability of the dual three-phase PMSM is utilized to the greatest extent.On this basis,aiming at the problem of fluctuation in fault operation,this paper also proposes an improved current loop control structure,which significantly improves the performance of the motor in fault operation.The proposed strategy and control method have theoretical reference and practical value for fault-tolerant control of the multi-phase PMSM.Firstly,based on the vector control,the mathematical model of dual three-phase PMSM is established.The motor system is decoupled by the static and rotating transformations,and the speed and torque switching control in the full phase operation state is realized by the vector control.On this basis,the mathematical model of dual three-phase PMSM under single-phase or multi-phase stator open-circuit fault is established.Following the principle that the magnetomotive force of the motor needs to be constant in operation,the optimal solution of the phase currents under fault operation is obtained by using the optimal condition of the minimum copper consumption of the stator.Taking the optimal solution as the control target,the new control objects are created by asymmetric coordinate transformation,and the current loops of vector control are built to realize the fault-tolerant control in an open-circuit fault system.Then,this paper unifies the fault-tolerant control strategies under different fault types and sums up the common points of the mathematical models of various asymmetric motor systems.It is proposed that the fault-tolerant control strategy for different kinds of faults can be formed only by modifying specific coordinate transformation matrix,the time-varying matrix in the voltage equation and harmonic subspace matrix.According to different fault types,the specific values of these matrices are solved to form the operable fault-tolerant control method.According to the different connection modes of the motor,the three-phase open-circuit situation adopts two control methods: method with neutral current and without neutral current respectively and compares the effect and influence of the two control methods on the system performance.Aiming at the problem that the system cannot be decoupled completely when using the proposed fault-tolerant control strategy,an improved vector control structure based on dual-layer current loops is proposed.It is analyzed that the stator resistance and phase leakage inductance,which are ignored by the traditional current loop structure for vector control,will make the system not completely decoupled and lead to index fluctuation.The time-varying part and the time-constant part of the voltage equation are separated and controlled respectively.Through the mathematical model of the motor system,the selection method of the parameters of the dual-layer current loops is obtained.The stability analysis of the fault system with the fault-tolerant control strategy and dual-layer current loops are carried out.The validity of the fault-tolerant control strategy to maintain the stability of the open-circuit fault system is proved theoretically,and the conclusion that the structure of the dual-layer current loops will not affect the stability of the system is drawn.Finally,the simulation model and experimental platform of the dual three-phase PMSM system are built.One or multi-phase open-circuit fault of the motor is simulated.The fault-tolerant control strategy and the dual-layer current loop structure are used to control the motor,so as to maintain the operation ability of the motor when the single-phase to four-phase open-circuit fault occurs.The feasibility of the fault-tolerant control strategy and the double-layer current loop theory is verified.