Research On Electromagnetic And Temperature Rise Characteristics Of Short-term And High Over-load Slot-less Tubular Permanent Magnet Linear Motor

Slotless tubular permanent magnet linear motor (TPMLM) takes the advantagesof non-transverse end, high winding usage, low cogging force, and so on. Itpossesses broad prospects in linear motion application. For the existing slot-lessTPMLM, the low magnetic load restricts the improvement of the thrustcharacteristic. Increasing the electric load is benefical to imprve thrust index. But,the temperature rises quickly and threatens the reliability, so estimate thetemperature rise is necessary. This paper focuses on the electromagnetic and thermalcharacteristics of the slotless TPMLM, which is applied in wide load servo system.The purpose is to improve the thrust characteristic, estimate the temperature riseaccurately to ensure reliability, and then inpromotes its application.Firstly, this paper calculates and analyzes the magnetic field of the slotlessTPMLM. On that basis, the particularities of the winding of the slotless TPMLM areresearched. According to the particularity that there is phase angle difference amongthe back EMFs of the windings in the different position in one virual slot, which isrelated to the insulation between phases, the virtual slot axial winding distributionfactor is proposed. Furthermore, the calculation formula is deduced to calculate theaxial distributional characteristic of the winding in virtual slot. According to theparticularity that the position of the winding belons to physical air gap, and thewinding thickness is closely related to the electrical and magnetic loads, the windingthickness is optimized and researched. And the laws that the winding thicknessaffects the thrust and the motor constant are gained.In terms of the drawbacks of big leakage flux and low usage of the stator iron,the similar trapezoid, convex, the similar V-shaped and the similar U-shaped polesare proposed based on the theory of flux concentrating and strengthening, and themagnetic fields of the motors are improved. The results show that the similartrapezoid and convex poles can enhance the magnetic field by increasing the widthof the stator iron near the outer diameter. The thickness of the permanent magnet forthe similar V-shaped pole is halved, which reduces the leakage flux circuit in thenon-magnetic axis for one thick permanent magnet. There is magnetic fluxconcentrating effect existing on the similar V-shaped pole. The similar U-shapedpole possesses the effect of both the magnetic flux concentrating and strengthening.The air gap magnetic flux is enhanced significantly without increasing the harmoniccomponents, so the thrust is promoted to a large extent. The research on the poleparameters reflects that the similar trapezoid and convex poles are more suitable forthe motor whose ratio of the stator outer/inner diameter is big, and the similar V-shaped and the similar U-shaped poles is beneficial to improve the magnetic loadfor the motor with the low ratio of the stator outer/inner diameter. The prototype isdesigned and manufactured, and the no-load back EMF and static thrust experimentare done.According to the difficulty of winding modeling in motor temperaturecalculation, the improved layered winding model for slotless TPMLM is established.Besides, the temperature rises of the circular winding sample with different highcurrent densities are calculated and tested, which can verify the rationality of thewinding model, revealing the law of the temperature distribution and rise of thehigh current density winding. The research provides reference for the selection ofthe winding current density. Aiming at the complexity of the air flow on the motorsurface and the heat transfer between the air and the motor, the dynamic gridmethod is adopted to establish the open fluid field of the tubular linear motor. Thelaws of air flow and heat convection on the mover outer surface and in the air gapare gained.The particularity of the heat exchange in slotless TPMLM is analyzed. And itis pointed out that the condition of the partial stator outside surface alternatesbetween natural convection and forced convection repeatedly. The combination ofthe thermal circuit and temperature field method is provided, which is applied to thetemperature rise calculation when the motor works in different conditions. Whenthe motor works in long distance, the mover temperature field and statortemperature field, and the thermal circuit model of the air gap are establishedseparately. Besides, the correlation between the temperature fields and air gapthermal circuit is built. When the motor works in short stroke, the temperature fieldof the coupled region of mover and stator is selected as the calculation region, andthe heat transfer from the coupling region to the uncoupling stator is equivalent tothe heat convection boundary. The equivalent heat coefficient can be calculatedaccording to the thermal circuit of the uncoupling stator. Through the method ofcombination of thermal circuit and temperature field, the calculation accuracy isimproved, and the model is simplified. The temperature rise of the motor inshort-term and high over-load condition is calculated, and the law of thetemperature gradient distribution and its variation is obtained. The temperature riseexperiments by both the dynamic and static methods are conducted, which verifiesthe studies above.The law and characteristic of the heat generation, heat absorption and heatdissipation when the motor works in high over-load condition are analyzed andsummarized. The method of increasing the heat absorption capability is proposed,aiming to minimize the high winding temperature rise for the short-term highover-load motor. Based on it, the insulation structure is optimized. The results reflect that although the absorbed heat increases, the temperature differencebetween the winding and other parts is reduced, and the winding temperature isreduced effectively. When the slotless TPMLM works in different conditions,including long time and short term states, the methods of heat conductionoptimization, enhancing heat dissipation, and reducing loss by the new polestructure are applied to reduce the temperature rise. Their effects are compared andanalyzed, guiding the choosing of reasonable thermal optimization methods toreduce the temperature rise.Through the above research, this paper obtained the method of improve thrustdensity by enhance magnetic and current load. Meantime, the objective of thetempearture calculation and thermal optimization research is to improve thereliability by estimating the high electric load winding temperature rise accuratelyand suppressing it.