Key Technology Research On Low Speed High Torque Proper Fraction-slot Concentrated Winding Permanent Magnet Motor

For low speed high torque proper fraction-slot concentrated winding permanent magnet motor(LCWPM) which span being 1 pitch, it is easy to realize inserting winding mechanically,and then, the inserting winding efficiency is increased, the quality is improved, the workforce is liberated and the cost of the motor is saved. There are a lot of advantages for LCWPM small stator winding, for example saving copper material and steel material, low copper loss, short axial length, small volume and high efficiency. Each stator teeth of LCWPM can be made into one unit module, and different stator tooth unit module can be separated. This method provides a new way to solve the large diameter motor transportation, installation and maintenance problems. The special structure of LCWPM, which makes its performance parameters different with the conventional motor, need to be further studied.The subject comes from the National Natural Science Foundation ‘Research on a novel low-speed and high-power synchronous machine with module combination stator’(51177106)and Science and Technology Department of Liaoning Province Plan Project ‘Mechanical equipment of low-speed and high-torque low-voltage and high power direct drive permanent magnet motor’(2011220036). The key technologies of LCWPM are the low-speed performance and maximum torque. This dissertation focuses on the study of cogging torque and ripple torque which makes LCWPM produce vibration and noise. And, the leakage reactance, especially slot leakage reactance and harmonic leakage reactance is researched which influence the maximum torque deeply. Some theoretical and practical conclusions are obtained, mainly including the following 5 parts.(1) The surface-mounted LCWPM cogging torque law with skewed slot(or skewed pole)distance is studied, and the cogging torque of 24-slot/20-pole and 72-slot/20-pole prototype is designed by finite element method(FEM). At the meantime, the effects of parameters such as no-load back electromotive force(EMF), current power factor, and the maximum torque multiple by skewed slot(or skewed pole) distance is researched. Skewed slot(or skewed pole)has an adverse effect on the efficiency, power factor and the maximum torque. With the skewed slot(or skewed pole) increase of the distance, the influence becomes larger. So, the minimum skewed slot(or skewed pole) distance should be chosen by design. There is morethan one skewed slot(or skewed pole) distance makes the cogging torque of LCWPM is 0, so,the skewed slot(or skewed pole) distance should be chosen according to the actual use of LCWPM.(2) The relationship between back EMF and ripple torque is studied. The results show that the ripple torque frequency is 6 times of the motor rated frequency. When??1616?kkEE ?k?,2,1??, 6k times ripple torque can be eliminated. When 5 subharmonic and 7subharmonic of back EMF are equal, 6 subharmonic torque which is the most favorable to weaken the ripple torque can basically be eliminated. Rotor field is a major cause of back EMF harmonics. Ripple torque can be weakened by optimizing the pole embrace to change 5,7 subharmonic electromotive force value.The pole embrace analytical expression is derived when 5 and 7 subharmonic back EMF is equal, and the result is verified by the finite element method. The theoretical basis how to select the pole embrace to reduce ripple torque is provided by the dissertation. Due to the neglect of the permanent magnet end leakage, the analytical calculation value is smaller than the finite element analysis value. There is not only one pole embrace value to when 5 and 7subharmonic back EMF is equal. The large pole embrace value is chosen in order to make the fundamental back EMF be high.(3) The magnetic lines of flux distribution in the stator slots are analyzed by the FEM.The results show that the magnetic lines of flux are substantially parallel to the surface of the armature. Energy method is used to study LCWPM slot leakage reactance, and the slot leakage reactance of analytic expression is obtained. Winding spacing how to affect trapezoidal slot and rectangle slot leakage permeance is studied. The slot leakage permeance of up-down distributed winding is larger than the left-right distributed winding.(4) A new method of “double star chart” is applied to cumulate LCWPM harmonic distribution coefficient. The analytical coefficient expressions of harmonics unit leakage permeance are obtained and the harmonics unit leakage permeance curves of LCWPM which could be applied to check are drawn with different slots per pole per phase. It shows that the expression of harmonic wave short-pitch factor is the same, but distribution coefficient is different, when the unit stator slot number respectively is odd,4mkQ0? ?k?,2,1?? and ? 122?0kmQ?? ?k?,2,1??. The harmonic wave short-pitch factor,distribution coefficient and winding coefficient are periodical change, and the change cycle isassociated with unit motor slot number. Because a large number of fractional harmonics exist,the harmonic leakage reactance of LCWPM is far greater than the conventional motor’s.(5) LCWPM electromagnetic design program is developed by Matlab. For comparison,72-slot/20-pole and 24-slot/20-pole prototype are designed and the leakage of the two prototypes is calculated. The results show that, the prototype leakage reactance makes up a large part of the synchronous reactance, especially the slot leakage reactance and harmonic leakage reactance. The test platform is established, and the prototypes cogging torque, ripple torque, efficiency, power factor, the maximum torque and reactance is tested. And the corresponding parameters of the two prototypes are compared, and the results show that the calculated values are in good agreement with test value, which verifies the theoretical analysis being correct. The influence of special structure of LCWPM on its performance is expounded.