Research On Parallel Direct-driven Conjoined Permanent Magnet Synchronous Motor For Twin-screw

Parallel synchronous counter-drive equipment is widely used in twin-screw vacuum pumps,twin-screw compressors,rolling and extrusion equipments,crushers and other mechanical equipments,which occupie an important position in the national economy.Taking the twin-screw pump as an example,the current driving method is the masterslave drive.A three-phase induction motor drives the master shaft to rotate.The master shaft drives the slave shaft to rotate in the same or opposite directions through the synchronous gear to complete mechanical work.Aiming at the outstanding problems caused by the "gear-driven" driving method,such as dynamic sealing of equipment,limited pump displacement,strict requirements for synchronization,short maintenance cycle,and large volume,this dissertation proposes a Parallel Direct-driven Conjoined Permanent Magnet Synchronous Motor for Twin-screw(PDC-PMSM),which is used to directly drive the twin-screw pump,eliminating the mechanical gear and simplifying the transmission system.According to the special problems brought by the new motor structure,this dissertation focuses on the research work from the aspects of its structure and operation mechanism,the magnetic field analysis between the two rotors,the PDCPMSM comprehensive design method,and the analysis method of system stiffness and dynamic characteristics.Then the theory is verified by prototype experiments.The main research contents include:(1)The basic structure and operating mechanism of the PDC-PMSM are studied.The PDC-PMSM consists of a conjoined stator and two synchronously rotating rotors,and the left and right windings are connected to the same power source.The combination rule of conjoined stator is analyzed,and the embedding rule of single and double layer windings in conjoined stator is compared.The current directions of the corresponding windings on the left and right are the same,and the polarities of the permanent magnets at the mirror symmetrical positions are opposite,generating a pair of reverse rotating magnetic fields to make the two rotors of the PDC-PMSM rotate synchronously and reversely.The area between the two rotors is named as the magnetic field interaction area,and the magnetic circuit characteristics of the magnetic field interaction area and the electromagnetic relationship of the motor at different positions of the two rotors are analyzed from time to time.(2)Comprehensive analysis of the PDC-PMSM overall design method.Determine the parameters of a single motor and combine the single motors into a PDC-PMSM.The influence of parameters of magnetic field interaction area on motor performance is analyzed.The design principles and method of PDC-PMSM are summarized,and a PDCPMSM with rated power of 2.2k W and rated speed of 4500r/min is designed,and the simulation analysis is carried out by using finite element software.(3)Due to the space asymmetry of partially-cut stators in PDC-PMSM structure,a no-load magnetic field analytical calculation model combined with curvature coefficient is proposed considering the large calculation amount of three-dimensional magnetic field finite element method.The calculation model is analyzed by using fourier series transformation,hyperbolic function and separation variable method.Considering the special structure between the PDC-PMSM rotors,the curvature coefficient is introduced to analyze and calculate the electromagnetic field.Finite element simulation and prototype experiment are used to verify the correctness of the analytical model,and the results show that the analytical model can be used for the magnetic field calculation of this special structure motor.(4)The gap between the twin-screws is small,and the vibration will cause the screw to deform or even directly damage.The stress calculation model of the PDC-PMSM twinscrew pump system is established.The stiffness of the twin-screw pump system and the twin-screw pump system with PDC-PMSM are analyzed to obtain the maximum deformation and the location of the maximum deformation.In order to study the resonance problem and carry out modal analysis,the natural frequencies of each order and the corresponding critical speed are calculated.The influence of bearing stiffness on critical speed is analyzed to judge whether screw stiffness and critical speed can meet the requirements of twin screw pump system.(5)A prototype machine of PDC-PMSM with 2.2k W was developed,and analyzed the structure of the prototype.The twin-screw pump was used as load end of the tested prototype,and assembled it into a direct drive system.The prototype developed was tested,including: winding inductance parameter test,no-load back EMF test,twin-screw synchronization test,measurement of the relationship between efficiency and power factor change with load rate,and overall efficiency comparison of the drive system.By comparing the experimental results with the simulation analysis,the correctness of the PDC-PMSM design theory and the comprehensive performance of the developed prototype are verified.