Research On Fault Model And Diagnosis Of Direct-drive Permanent Magnet Synchronous Motor

Due to its various advantages such as high torque density,high power density,high efficiency and so on,direct-drive permanent magnet synchronous motor(DDPMSM)is widely used in hoists,robots,electric vehicles,high-end manufacturing equipment,national defence industry and other fields.However,owing to the complicated working conditions,such as overload and impact,and the harsh working environment,DDPMSM is prone to turn-to-turn short circuit fault and demagnetization fault.The failure of the drive motor in the related application fields not only affects the economic benefit of the enterprise,but also threatens the equipment and personal safety.Early fault detection and fault diagnosis are an important means to avoid the deterioration of the fault of the DDPMSM and to improve the operation safety and reliability of the system.Therefore,the research of the early fault detection and fault diagnosis of the DDPMSM has important theoretical research value and engineering application value.In this paper,taking DDPMSM as the research object,the mathematical models of stator winding fault and demagnetization fault were established respectively,and the effects of different faults on motor performance and key parameters were studied.Then,the fault cause and fault mechanism were analyzed,and the fault characteristic quantity of DDPMSM turn-to-turn short circuit fault and demagnetization fault was selected.Besides,the research on the mechanism of multi-factor coupling effect on motor performance during internal short circuit of coil element was taken,the method of DDPMSM fault detection,fault type identification and fault location suitable for different conditions was proposed and the experimental research work was carried out.The specific contents of the study are as follows.A unified mathematical model of DDPMSM in health state and stator winding fault state based on coil units was proposed.Firstly,considering the influence of winding type and short circuit coil position on the inductance and fault characteristics of motor,each coil is divided into several units,and a unified mathematical model of stator winding in health and fault state based on coil units was established.Secondly,considering the spatial position of the short circuit in the coil element and the actual winding process of the winding,a fine modeling method of DDPMSM coil units inductance was proposed.Finally,by using the proposed mathematical model,the physical quantities such as phase voltage,coil voltage,branch current and output torque in health state and stator winding fault state were compared and analyzed in detail.And compared with the finite element results,the correctness and accuracy of the unified mathematical model proposed in this paper were verified.It can provide a friendly interactive interface,which is convenient to analyze the running performance of motor under healthy state and different types of stator winding fault state without changing the topology of the model,and can accurately analyze the turn-to-turn short circuit fault in the coil element.A method for early fault detection and coil positioning of DDPMSM turn-to-turn short circuit based on branch current and two-stage PNN was proposed.Based on the proposed unified mathematical model,the variation of stator current,stator voltage,electromagnetic torque and other physical quantities before and after turn-to-turn short circuit fault of coil elements under different working conditions,as well as the influence of short circuit turns on sensitive fault characteristics,were compared and studied,and the branch difference current and branch current residual were determined as fault characteristics quantity.In addition,the construction method of characteristic vector for turn-to-turn short circuit fault branch and coil positioning was proposed.Combined with two-stage PNN neural network algorithm,the real-time early fault detection of DDPMSM turn-to-turn short circuit and the automatic and accurate positioning of short circuit coil were realized.The paper studied the effects of short circuit turns,short circuit position and fault resistance on motor performance and fault characteristics.Based on the unified mathematical model,the effects of short circuit position,short circuit turns and fault resistance on the key parameters such as fault current,branch current and stator voltage were compared and studied,and the output performance of DDPMSM under multi-factor coupling was analyzed.The results show that under the same number of short circuit turns and the same fault resistance,different short circuit positions have great influence on the current,torque fluctuation and double frequency torque of the fault coil,and the short circuit position has a great influence on the current,torque fluctuation and double frequency torque of the fault coil.If the number of short-circuit turns is less and the fault resistance is smaller,the short-circuit position has a greater influence on the characteristics of the motor.The limitations of judging the severity of turn-to-turn short circuit fault by the number of short circuit turns and fault resistance were revealed,which provided a theoretical basis for the evaluation of the degree of turn-to-turn short circuit fault.An extraction method of demagnetization fault characteristic quantity based on a new detection coil and a no-load EMF residual demagnetization permanent magnet positioning method based on magnetic pole partition and three-stage PNN were proposed.The installation,arrangement and detection mechanism of the new detection coil were studied.The extraction algorithm of no-load back EMF residual under the influence of many factors,such as magnetic circuit saturation,demagnetization degree and parallel branch circulation,was proposed.The characteristic vector of demagnetization fault with the peak position,peak number and peak ratio as the key information parameters of no-load back EMF residual in an electric cycle was constructed.The partition was carried out according to the principle of minimum number of detection,and the real-time detection of demagnetization fault and the fast and accurate positioning of demagnetized permanent magnet were realized by combining the three-level PNN algorithm.Through developing the DPMSM fault simulation prototype,designing the fault test scheme for stator winding and building DDPMSM experimental test platform,the experimental test and verification were carried out.The experimental results are in good agreement with the theoretical analysis results,which shows the correctness and effectiveness of the unified mathematical model of stator winding in health state and fault state,and verifies the feasibility and effectiveness of the selected fault characteristic quantity.