Research On Five Phase Open-winding Drive System And Its Fault-tolerant Control

With the increasing environmental pollution and energy shortage,the development of electric vehicles has become an important way to solve this problem.As the energy conversion carrier and the execution component of the electric vehicle,the motor drive system is directly related to the safety of the operator.Therefore,in recent years,high reliability motor drive systems have been paid much attention.Compared with three-phase motor drive systems,the five-phase open winding motor drive system has outstanding advantages in fault tolerance,power density,efficiency and output level,making it more suitable for electric vehicle applications.Based on the features of five-phase open-winding motor drive system,a five-phase permanent magnet fault-tolerant open-winding motor is investigated,including the basic modeling method,modulation strategy,zero-sequence current suppression strategy,fault diagnosis and position of the power device,which provides an important technical basis for improving the reliability of the five-phase open winding motor drive system.The main research of the thesis include the following aspects:1.The characteristics of the five-phase open winding motor drive system in terms of power supply mode and topology are revealed.The operating principle of the five-phase open winding motor is analyzed,and the mathematical model of five-phase open winding motor is established both in fundamental and the third harmonic plane.The space voltage vector of the five-phase open winding motor in the fundamental plane and the third harmonic plane is also shown.The simulation platform of the fivephase open winding motor drive system is built,which laid the foundation for the subsequent research.2.The zero-sequence current suppression strategy of the common DC bus type five-phase open winding motor drive system is developed.Firstly,the zero sequence current caused by the dead zone effect of the inverter is analyzed.Secondly,by introducing feedback control to zero-sequence current and the driving of the modulation strategy,the reference zero-sequence voltage and the duration time of zerosequence voltage vector of each inverter can be obtained,and thus the modulation of the zero-sequence voltage can be achieved.Finally,the modulation range under the zero-sequence current suppression strategy is analyzed,and the effectiveness of the zero-sequence current suppression strategy is verified by simulation and experiment.3.The open-circuit fault diagnosis technology of the power switch with five-phase open-winding dual inverter is studied,and a fault diagnosis method based on the third harmonic residual is proposed.The determination of the open circuit fault is realized by monitoring the third harmonic residual component in f?3N-f?3N stationary coordinate.Based on the relationship of the residual component,the fault phase and fault current can be identified.Due to the particularity of the open winding topology,when the power switch has an open-circuit fault at the symmetrical position,the system will exhibit the same characteristic performance,which will bring difficulties to the accurate positioning of the faulty switch.For this reason,an online small current pulse test approach is proposed.This approach is used to accurately locate the open-circuit switch within the fault phase,and the proposed method can accurately control the amplitude and phase of the test current,thereby improving the safety of the fault diagnosis method.Simulation and experimental results show the accuracy and robustness of the diagnostic method.4.The diagnosis method of the inter-turn short-circuit fault of the five-phase open winding motor and the corresponding fault-tolerant control strategy are developed.By establishing a five-phase open winding motor model under inter-turn short-circuit fault,a on line fault diagnosis method based on amplitude detection of second harmonic ripple component in torque difference is proposed,and based on this,a fault-tolerant control strategy under inter-turn short-circuit fault is proposed.The control strategy achieves fault-tolerant operation by compensating the current in the d-q coordinate.According to the characteristics of the open-winding motor,the calculation of the product of the short-circuit current and the short-circuit turns is converted into the zero-sequence current,which greatly reduces the calculation amount and improves the accuracy of compensation.5.To avoid current of the fault phase exceeding the limit value,a fault-tolerant control method based on active open phase is proposed.The fault-tolerant control strategy can be divided into two parts,one is for the open phase fault,and the fault-tolerant control is realized by the decoupling matrix.The other is for the inter-turn short-circuit fault,and the fault-tolerant control is achieved by the compensation shortcircuit current in d-q axis,and the compensation can be obtained by the zero-sequence current and the zero-sequence voltage.By combining the two parts of the fault-tolerant control strategy,the undisturbed operation of the motor drive system after the fault is realized.6.Based on DSP28335,an experimental platform for five-phase open winding motor drive system is built.The hardware drive circuit is designed,and the extraction of the motor winding tap is completed,and thus the accurate simulation of various faults can be realized,which lay the foundation for this topic and subsequent research.