| Recently,permanent magnet machine has been generally applied in all kinds of areas of the society due to its advantages,such as simple structure,high reliability and energy saving.Furthermore,the demands for functions of permanent magnet machines are getting higher and higher,and their various performance indicators have also become an important object of industry attention and research.Bearing,as an important part of the motor,plays a vital role in the stable operation of the motor.Serious damage to the bearing may lead to the loss of stability of the entire motor system.Therefore,it is necessary to study the stability and reliability of the motor bearing.The most common reason for bearing damage is natural aging,as well as excessive temperature,installation problems,load vibration,bearing electrical corrosion problems caused by shaft voltage and shaft current.Bearing electrical corrosion caused by shaft voltage is a very important reason for bearing damage.At present,the research on shaft voltage is not rare,but in the existing research on shaft voltage,most of them take asynchronous motor as the research object.In addition,they mainly study the mechanism of shaft voltage generation under no-load magnetic field and weaken the shaft voltage by external measures.However,there is a lack of research on the shaft voltage of permanent magnet motor,a lack of methods to suppress the generation of shaft voltage from the motor design itself,and a lack of research on shaft voltage of armature magnetic field of permanent magnet machine.In this paper,the no-load magnetic field of permanent magnet machine considering the stator chute is analyzed,and the analytical model of no-load shaft voltage considering the stator chute is derived.Then the relationship between the no-load shaft voltage and pole and slot number combinations is given,and the effect of stator chute on no-load shaft voltage is analyzed.Then this paper mainly analyzes and deduces the armature reaction shaft voltage of permanent magnet machine when the stator winding is energized,and the condition when three-phase current is not symmetrical is analyzed,and finite element method is used to verify the results.The shaft voltage of integer slot permanent magnet motor caused by rotor eccentricity is analyzed,and optimal pole-arc coefficient and stator chute method are studied to weaken eccentric shaft voltage.The specific research contents are listed as following:(1)The no-load magnetic field of permanent magnet machine is analyzed,machine failure is not considered and the armature magnetic field generated by the current of stator winding is not considered.The no-load magnetic field of the machine with stator chute structure is analyzed only under the effect of permanent magnet,and the analytical expression of no-load shaft voltage with stator chute is deduced.According to the expression of no-load shaft voltage and its generating conditions when chute is considered,the relationship between no-load shaft voltage and the combination of number of pole slots is analyzed,and seven permanent magnet motors with the same power and similar structure are established for simulation verification,and the results are consistent with the analytical derivation.Then,the influence of stator chute on shaft voltage is analyzed,and the optimal number of stator chute which could effectively weaken the main harmonic components of the no-load shaft voltage is deduced by analytical method.Then,the finite element model was established in Ansoft for verification.(2)The load magnetic field of permanent magnet machine is analyzed without considering machine failure and the magnetic field generated by the permanent magnet,only under the impact of armature winding.Armature magnetic field is analyzed and deduced with or without considering stator core saturation and magnetic leakage.Firstly,without considering saturation and magnetic flux leakage,armature winding produces armature magnetomotive force.Then based on the magnetomotive force and magnetic permeability method,the air-gap flux density without considering magnetic saturation and magnetic leakage factors is obtained.Next,considering the effects of saturation and flux leakage on magnetic field,the factors are analyzed by finite element method,and a new distribution function is proposed to be equivalent to effects of saturation and flux leakage.And,based on the magnetic circuit principle,the air gap magnetic density under the action of armature magnetic field is deduced.Then,the net magnetic flux which varies only with time and is independent of position is analyzed,the armature reaction shaft voltage is obtained by Faraday’s law of electromagnetic induction,and harmonic components of armature reaction shaft voltage are analyzed.Then the 2D finite element models are established for simulation and verification.Fourier decomposition of shaft voltage obtained from finite element analysis is carried out,the results are consistent with analytical results.(3)Analyze the armature magnetic field in the case of three-phase current imbalance due to machine or line failure,without considering the magnetic field generated by the permanent magnet.Based on the symmetric component method,the asymmetric current is decomposed into three groups of symmetrical components,and the magnetomotive force generated by each group of symmetrical sequence current is analyzed.The air gap magnetic density generated by each sequence component is deduced with or without considering magnetic saturation,and the combined magnetic density is obtained by superposition,thus the shaft voltage under the asymmetric condition is deduced.Then the harmonics of shaft voltage increment in the asymmetric case are analyzed,and compared with harmonics of shaft voltage when three-phase current is symmetrical.The frequency characteristics of armature reaction shaft voltage are obtained when three phases are not symmetrical due to a fault.Finally,models are established in Ansoft for simulation and verification.(4)The no-load shaft voltages of the integer slot permanent magnet machine with static and dynamic eccentricity are deduced and analyzed,and verified by finite element method.Then,for the eccentric shaft voltage of the integer slot permanent magnet machine,the optimal pole-arc coefficient method is used to reduce higher harmonic components,and the optimal pole-arc coefficient is obtained by combining the analytical method and finite element method.And the stator chute method is used to reduce higher harmonic components,and the optimal chute number is obtained by combining the analytical method and finite element method. |
