Research On High-speed PMSM With Toroidal Windings For Driving Pulsed Alternator

Pulsed alternators are regarded as one potential pulsed power for electromagnetic weapons in the future.As a key component of the pulsed alternator power,prime motor plays an important role in achieving miniaturization of the power and transferring to actual combat.The prime motor should has the characteristics of flat structure,impact resistance and high power density,so that the conventional highspeed motors are not suitable for this application.In order to increase the power density of the integrated pulsed alternator,in which the pulsed alternator and the prime motor are mounted on a common shaft,and considering the dynamics problem of the high-speed shaft system,the prime motor should be designed as flat structure.It is a great challenge to carry out the structure design and improve the power density of the flat-structure high-speed permanent magnet synchronous motor(PMSM).The mechanical restriction and suitable winding type were studied for the flat-structure high-speed PMSM.A flat-structure high-speed PMSM with toroidal-windings was provided,avoiding the problems of long ends for lap-windings and high eddy-current loss for concentrated windings.The choice of the materials and design of the parameters influencing the power density were investigated on basis of two-dimentional(2-d)finite element analysis(FEA)method.Power density could be improved by use of the materials of low specific core loss.By division of the stator of toroidal-winding motor and use of the lightweight and non-magnetic materials of the outer stator,the power density could be improved.In addtion,the techoniques of low-conductivity sleeve material,decreasing notch width and increasing airgap length were studied to reduce the eddy-current loss density of the rotor,and further improve the power density.The influences of pole-arc coefficient and magnetization direction of magnets on the current curve and torque ripple were analyzed.Heating is the main factors limiting the high power density of the motor.In order to increase the power density and analyze the distribution of the temperature field,the losses of the toroidal-windings motor were analyzed,and methods to reduce the key losses were studied.The FEA models for analysis of the high-frequency AC losses of toroidal-windings were built.The influence of leakage flux resulting from the windings in the outer slots on the copper loss was analyzed.The results show that the problem of the high-frequency AC loss of the windings was very serious and the loss of the effective part of the windings occupies a small portion of the total copper loss.Therefore,the methods of division of stator and use of non-magnetic material of the outer stator and increasing strand number of the conductors were used to reduce the stator loss.The eddy-current losses of the rotor were calculated by threedimentional FEA method to take the nonuniform distribution of eddy current along axial directon into consideration.The sleeve loss occupies a larger portion of the total eddy-current loss of the rotor.And there is some eddy-current loss in the metal pole fillers.Hybrid structure of the sleeve,segmentation of magnets and modification of pole filler materials and structure were studied to reduce the rotor loss.The influences of these methods to reduce the partial losses on the total loss were further analyzed and the effect of the switching frequency of inverter on the losses was also studied.The contact area between the stator and water jacket is greatly reduced by slotting on the outer surface of the stator for the flat-structure high-speed PMSM with toroidal-windings.So the effect of the water cooling is greatly reduced.Moreover,the rotor cooling would be more difficult for thicker sleeve.In order to ensure the relibable operation,the cooling scheme suitable for the motor was studied.A computational fluid dynamics(CFD)model of the motor with water cooling and forced air cooling was first established for analysis of the temperature field.Through the method of the multi-field coupling of the electromagnetic field,fluid field and temperature field,the influencing factors on the temperature field were then analyzed,in terms of the motor structure,processing technology and driving mode.The measures of the improved ventilation structure,filling thermally conductive adhesive and water channel moving inward to outer stator were studied to solve the problems of the large volume and noise of the blower caused by the small airgap as ventilatting duct,and the high temperature rise caused by the large thermal contact resistance.Finally,a new cooling structure combining water channel moving inward to outer stator and ventilation in the inner slots was proposed.Because all the water channel walls are next to heat source,the cooling effects are better.Not only the volume of the motor and the noise of the system were reduced,but also the power density was increased.The problem of the strength is very serious for the high-speed rotor of the prime motor,because it is subjected to three kinds of forces including the discharging impact,high-speed centrifugal force and thermal stress caused by rotor heating.Based on elastic mechanics,the analytical model of the rotor strength subjected to discharging impact was built and the distribution of the rotor stress was analyzed.The results show that the rotor could be destroyed on the contact surface between different components.Increase of the contact pressure was thought usefull to improve the ability of impact resistance of the rotor.The effect of discharging impact on the shaft was also analyzed.The largest shear stress and the relative torsion angle of the shaft should be within the allowable range to keep the safety.The 2-d FEA models of the rotor strength subjected to centrifugal force and thermal stress were also bulit.The problems of the design and choice of the parameters related to the rotor strength were studied.The contact pressure can be increased by the increase of the interference fit and sleeve thickness and decrease of the rotor diameter,in turn,the ability of the impact resistance of the rotor can be improved.In addtion,the bending stress of the carbon-fiber sleeve could be resulted in by different strains of the magnets and pole fillers subjected to centrifugal force and thermal stress for the actual rotor,which will hinder the normal operation of the rotor.The stress of the rotor was analyzed through the three-dimentional FEA model of the rotor stress coupled with the model of temperature field.The influences of pole filler materials on the rotor stress were compared.A small-scale prototype was manufactured.Through the high-speed test,comparison of simulation and test results of the electromagnetic performance and tempature rise,the corrections of models for design and calculation,and the feasibilty of the proposed structure and technologies were verified.