Research On Fault-Tolerant Control For Open Winding Less-Rare-Earth Hybrid Permanent Magnet Brushless Motor

With the increasing concern of energy crisis and environmental pollution,electric vehicles(EVs),as an important way to alleviate energy crisis and environmental pressure,have attracted more and more attention.Permanent magnet motors(PMMs)have been widely used in the field of electric vehicles because of their high torque density,high efficiency and good dynamic response.However,rare earth permanent magnets(REPMs),as an important strategic resource of the country,are closely related to the national economy and people’s livelihood.In order to reduce the consumption of rare earth materials,less rare earth permanent magnet motors composed of rare earth materials and non-rare earth materials have become one of the hotspots of current research.In addition,the voltage of EVs is limited by the capacity and voltage level of the battery on board,which restricts the speed range and power density of the motor to a certain extent.The topology of dual inverters with common DC bus can improve the output power and wide the speed range of the motor when the battery capacity of EVs is limited.Its application in the motor drive system has attracted wide attention.Moreover,the reliability and fault-tolerance of driving system,which is the core components of EVs,are directly related to the safety of drivers.Therefore,it is of great significance to study fault-tolerant control for hybrid permanent magnet material brushless(HPMM-BL)motor in dual inverter.Firstly,this thesis introduces the stator and rotor structure of hybrid permanent magnet material brushless motor and establishes the mathematical model of dual inverter according to the characteristics of back EMF of HPMM-BL motor.Meanwhile,in order to reduce zero-sequence current in dual inverter with common DC bus,the zero-sequence current controller based on plug-in repetitive control(RC)is proposed.The periodic change of zero-sequence current in the system is restrained by the closed-loop control of zero-sequence current,and the parameter tuning process of RC controller is given.Although the zero-sequence current suppression strategy can effectively reduce the zero-sequence current problem,the modulation range of the open-winding system will be reduced correspondingly.Therefore,the phase-shift decoupling modulation strategy is proposed in this thesis.Based on decoupled modulation,the angle between the voltage vectors of two inverters is taken as a control variable.The method can be used to obtain a wide speed range and a low zero sequence voltage simultaneously,which simplifies the modulation strategy.Secondly,a new fault-tolerant control method based on the principle of leg-multiplexing is proposed in this thesis,because the current fault-tolerant control methods don’t make full use of the redundancy of dual inverters and the speed range of motor in fault-tolerant mode is low.Four corresponding fault-tolerant topologies and their modulation strategies are presented.By comparing four fault-tolerant topologies,the optimal fault-tolerant control method is obtained,which has high speed range.Then,this fault-tolerant method is extended to two-leg fault condition,and an unified fault-tolerant topology and corresponding fault-tolerant modulation strategy are obtained.Moreover,two zero-sequence voltage suppression strategies based on dead-time compensation and RC controller are proposed,which effectively solve the influence of zero-sequence voltage under fault-tolerant mode.Finally,the experimental platform of open winding HPMM-BL motor with common DC bus based on dSPACE DS1007 is built to verify the proposed algorithm.The simulation and experimental results are given to verify the effectiveness and correctness of the proposed algorithm.