Research On Low-Speed And High-power Permanent Magnet Machine With Modules Combination Stator

In recent years, low-speed and high-power permanent magnet machine direct drive technology has been gained comprehensive attention in mining, petroleum, metallurgy, ship propulsion, wind generators, etc. Low-speed and high-power machine must have the characteristics of low-speed and high-torque machine, while the torque is proportional to the effctive volume. Therefore, low-speed and high-power machine usually has a very large volume. The large volume of machine brings enormous difficulties in manufacturing, transportation, assembly and maintenance. Based on the National Natural Science Fundation Project of China "Research on a novel low-speed and high-power synchronous machine with modules combination stator"(Grant No.51177106), aiming at the problems existing in the manufacturing, assembly, maintenance and poor fault tolerance, a novel low-speed and high-power permanent magnet machine with modules combination stator(MCSLSHP-PMM) based on unequal span winding was proposed. According to the special problems of this novel machine structure, the characteristics and mathmatical model, key technologies and design methods such as stator partitioning principle and q selection method of unequal span winding, influences of unequal span winding for motor performances and coil end force, source of end cogging force and its weaken methods were studied. Finally,the theory was verified by prototype machine experiments. The main research results are as follows:(1) The structure and principle of MCSLSHP-PMM were studied. For two cases of all modules or partial modules putting into operation, the voltage equation and electromagnetic torque equation of MCSLSHP-PMM were established. The advantages and disadvantages were compared between module machine windings adopting series and parallel power supply modes, which provided basis for MCSLSHP-PMM power supply and drive system selection. Easy maintenance as one of the major features of this machine structure, and considering the convenience of fault stator module disassembly, a assembly method of stator modules external assembled was presented.(2) The key design technologies of MCSLSHP-PMM were studied. The stator partitionning principle and slots per pole per phase q selection method of unequal span winding were analyzed. A novel surface mounted magnetic pole structure composed of rectangular shape permanent magnet and magnetic conductive metal block was put forward, the relationship between magnetic metal block outer arc shape and harmonics distortion of air-gap flux density were studied, and the metal outer arc shape was optimized by adopting genetic algorithm. Eddy current loss of magnetic poles adopting the conventional and novel pole structures were calculated. Then, the general design method of MCSLSHP-PMM was summarized and electromagnetic design CAD software was compiled. Finally, a prototype machine was developed and electromagnetic field simulations were analyzed by finite element method.(3) Taking prototype machine of MCSLSHP-PMM as the research object, influences of unequal span winding for motor performances and coil end force were studied. By using equivalent magnetic circuit method and incremental inductance method, the self-inductance and mutual-inductance parameters of prototype were calculated respectively, and the effect of unequal span winding of machine performances were analyzed by adopting phasor method. Then, the elimination methods of three-phase winding inductance parameters inconformity caused by each branch of per phase containing unequal large sapn coils and small span coils were summaried. Finally, the end winding finite element model of MCSLSHP-PMM prototype was established, taking coils end as a whole, the radial electromagnetic force of each coil end varying with time was studied. Based on magnetic and solid co-simulation mathod, the radial electromagnetic force distribution and stress of each part of large span coil were analyzed, which provided theoretical basis for fixing and binding of unequal span winding end.(4) The source of end cogging force and its weaken methods were reaearched. By using Schworz-Christistoffel transform theory, the cogging effect and end effect were analyzed respectively, and formation mechanism and weaken method of cogging torque were studied. The three weaken methods of end cogging force, including stator module width optimization, stator core sectional dislocation along axial and end cogging forces offset between stator modules, were focused on research, which provided references of improvning the stability and control precision of system operation. For the three weaken methods, the first two methods were studied on a single stator module, and the last method was studied on the overall machine. Finally, the method of reducing torque ripple caused by the incomplete asymmetric mutual-inductance parameters in the single module or among the modules when partical stator modules put into operation was studied.(5) A prototype machine of MCSLSHP-PMM with 12 k W and three modules was developed, and experimental studies were carried out by building a test-bed. The main contents of experiments included: winding inductance parameters measurement, no-load EMF waveform measurement, relationship between torque and modules number, current waveforms and phases under no-load and full-load and efficiency and power factor changed with load rate measurement under different speeds and different modules put into operation. Compared with experimental results and simulations, the corretness and rationality of key technologies and general design methods were partially verified.