| The permanent magnet synchronous machine(PMSM)has many advantages,such as high power density,high efficiency,high torque-inertia ratio,wide range of speed control with constant power,low vibration and low noise,so it has been widely used in many fields.However,there exist disadvantages in PMSM.The magnet source of excitation field in PMSM mainly comes from the permanent magnet poles,therefore there does exist a demagnetization risk for magnets,and then the output performance and service life of the machine will be decreased.Consequently,it is necessary to study the internal electromagnetic field,rotor unbalance magnetic pull and the temperature field under the condition of failure,which is of great significance in finding out the influence mechanism of failure on the machine performance and in supporting the failure diagnosis of PMSMs.In this paper,the analytical models in different physical fields under ordinary failures,including loss of excitation,inter-turn short circuit in stator winding and rotor eccentricity,are established to determine the mutual influence and relationship between the physical fields,to reveal the influence mechanism of failure on the key performance of machine,by which the characteristic signals as failure occurs will be found out,and a solid theoretic foundation of PMSM failure diagnosis will be laid down.The main contents and contribution of this paper are as follows.(1)The research is followed a PMSM with the rated power of 14 kW and rated speed of 2000 rpm.The finite element analysis(FEA)method is adopted to establish an electromagnetic field model of a PMSM with the field failure.A comparative study between normal status and loss of excitation is undertaken to explore the changes of machine performance in different ratio of demagnetization,and to reveal the mechanism of parameters change,including harmonic field,power factor,efficiency,loss,maximum torque,overloading capacity,and so on.The change of loss in different part of rotor under different loss of excitation is compared,the corresponding relationship between the harmonic field and loss is determined,which lays a foundation for the future analysis on the temperature field inside of machine.The test research on the loss of excitation of PMSM is undertaken,the output parameters of machine under different rotation speed and different loads are measured,the proposed methods and the reliability of the results are verified,all of which provide important support for the failure diagnosis of PMSMs.(2)The FEA models of single-phase winding inter-turn short circuit failure and two-phase winding short circuit failure are established to study the influence of winding failures on the electromagnetic field and the operation performance.A method to determine the asymmetry of current in faulty winding is proposed,also this method is used to measure the influence of short circuit on the armature current.Based on the analysis of the field in machine,the changing mechanism of the output torque,torque fluctuation,input current,current asymmetry,power factor and the loss at different parts of the machine during the inter-turn short circuit in single-phase coil is revealed,also the change rules of the parameters mentioned above under different degrees of short circuit failure are provided.Additionally,the influence of partly short circuit in two-phase winding on the machine performance is studied,also the features of the air-gap magnetic fields under different types of short circuit in machine windings are analyzed,the corresponding variation relationship between the failure position and the air-gap magnetic field is provided,which lays a foundation for the diagnosis of the stator winding failure.(3)The FEA models of eccentricity failure,including static eccentricity and dynamic eccentricity,are established to study the influence of rotor eccentricity on the machine performance and the electromagnetic field.A FEA method to calculate the magnetic field and loss under different degree of rotor static and dynamic eccentricity failure is proposed.The harmonic field in the air gap is decomposed by using Fourier harmonious decomposition theory,the influence mechanism of rotor eccentricity on the machine loss is disclosed,which lays a foundation for researching the changes of temperature distribution at different part of machine.In this paper a concept of torque fluctuation factor is proposed to measure the influence of rotor eccentricity on the output torque,which describes the change rules of the torque fluctuation under different eccentricities.Because it is difficult to measure the distribution of the air-gap flux density along the circumferential direction,a detection method by using surface mounted coils is proposed to test the distribution of the air-gap flux density,which verified the previous analysis of influence.(4)The magnetic vector potential is adopted to analyze the electromagnetic force at rotor eccentricity,and the analysis model of rotor unbalance magnetic pull is established.The comparative study of the influence on unbalanced magnetic attraction force caused by rotor eccentricity is undertaken by FEA.By determining the rotor eccentricity,the changes of the unbalanced magnetic attraction force on rotor under different rotor eccentricity is provided,also the corresponding relationship between the rotor unbalanced magnetic attraction force and eccentricities is determined.The rotor unbalance magnetic pull under the loss of PM excitation and the failure of stator winding is studied,the changing mechanism of the unbalanced magnetic attraction force under different failure status is revealed by analyzing the harmonic field.(5)With the loss analysis of the PMSM under different faulty status and the heat transfer theory,a 2D temperature field calculation model of the PMSM is established.The temperature field in PMSM is calculated under the preconditions of defined boundary conditions,the temperature distribution at different parts of the PMSM and the temperature-sensitive characteristics of PMSM are studied.The change rules of the temperature distribution inside of the machine caused by different failures,such as loss of excitation,short circuit of the stator winding and rotor eccentricity,is analyzed by comparison.The influence of different failures on the temperature distribution in machine is provided,which reveals the temperature change mechanism at different parts of machine,and lays a foundation for preventing the excitation loss of the permanent magnet at high temperature and for the online temperature failure diagnosis of the PMSM. |
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