Thermal Field Analysis of Permanent Magnetic Brushless DC Motor for High Vacuum Condition

Permanent Magnetic Brushless DC Motors with advantage of high powerdensity, high torque/volume radios and high reliability, have been widely used inthe industrial production and daily life. Particularly in some special fields such asaerospace application, military areas, the power density and reliability of the motorare paid attention. In this paper, thermal behavior of BLDC motors applied in highvacuum condition have been studied, including calculation of motor losses, thermalanalysis of motor and motor test in high vacuum condition.The calculation methods of core losses are adopted to compare the classicalformula method, the classic separation of iron losses method and ellipse method.The characteristic of stator magnetic field is analyzed, and then ellipse method isapplied to calculate the stator core losses. It is also discussed that the variation ofwinding current impacts on core losses. PM eddy current loss is taken into accountconsidering thermal problems due to motor running under the high vacuumcondition. The corresponding principle of PM eddy loss is carried out in order toanalyze generation causes of eddy losses, which is calculate based on finite elementanalysis (FEA) method.On the basis of lumped parameter thermal circuit model, BLDC Motor thermalcircuit topology is obtained and its design features are analyzed under naturalconvectional condition. The simplified thermal circuit topology on the high vacuumcondition is obtained from the above circuit topology in according to radiationheat-transfer theory. The radiation heat-transfer coefficients for external and insidemotor surfaces are calculated through the simplified topology. In addition, thispaper analyzes some main factors which influent heat transfer, includingenvironment temperature, surface emissivity, and view factor.The research on temperature field of Permanent BLDC motor under highvacuum condition has been done. The thermal behavior of ring structure issimulated through FEA method in order to gain the distribution characteristic ofthermal radiation field. Then calculation and simulation of the motor stator averagetemperature rise has been done on different surface emissivity. It is found thataverage temperature rise is sensitive to the surface emissivity. Furthermore, the thermal performance of BLDC motor is calculated considering influence of statorcore loss and PM eddy current loss.The radiation heat-transfer tests on BLDC motor have been done for highvacuum condition. The core loss from experiment shows good agreement withellipse method, which verifies the reasonableness of core loss calculation.Temperature rise of motor windings and frame at different degree of vacuum havebeen tested, and it is observed that surface heat-transfer coefficient also decreaseswith degree of vacuum increased.