| The direct drive system with linear motor as the core can directly convert electric energy into linear motion mechanical energy,which is highly suitable for the field with linear motion demand.The linear motor direct drive system eliminates the intermediate transmission mechanism between the motor and the workbench,which effectively improves the overall efficiency and integration of the system.The cylindrical linear motor has the advantages of easy to overcome unilateral magnetic pull,no lateral side effect and high winding utilization efficiency,so it is especially suitable to be used as the power source of submersible progressing cavity pump in rodless oil production system.However,due to the structural characteristics of the linear motor itself,it has the defect of large thrust fluctuation,which is caused by the side effect,groove effect and three-phase asymmetry of winding parameters.In this paper,the rodless oil production system is taken as the research background,and the key issues such as pole slot fit of submersible permanent magnet synchronous linear motor,source and weakening measures of thrust fluctuation,and multi-objective optimization of the motor are studied,mainly including the following contents:Firstly,the pole slot fit and winding distribution of the cylindrical permanent magnet synchronous linear motor are studied.Based on the theory of unit motor,the optional range of pole slot fit of cylindrical permanent magnet synchronous linear motor is studied.Aiming at the special cake windings of cylindrical linear motor,the phase separation method and winding coefficient calculation method are studied by using the star chart of slot electromotive force,and the main factors affecting winding coefficient are analyzed.Finally,the linear motor model with different pole slots is simulated by finite element analysis to verify the correctness of theoretical analysis.Secondly,the source and weakening measures of thrust fluctuation of cylindrical PMSM are studied.Compared with rotary motor,cylindrical linear motor not only has thrust fluctuation caused by electromotive force harmonics and cogging force,but also has thrust fluctuation caused by stator core break and stator winding three-phase parameter asymmetry.In this paper,various sources of thrust fluctuation are analyzed theoretically,and corresponding weakening methods are proposed for each source.Aiming at the thrust fluctuation caused by harmonic emf,optimization of pole-slot fit,stator core segmentation and non-uniform air gap are adopted to reduce it.Optimization of polar arc coefficient,axial section of stator core and fractional slot are used to reduce the cogging force.The edge force is reduced by optimizing the length of stator core.Aiming at the three-phase asymmetry of windings,edge end teeth are added to improve it.Finally,taking the 36-slot linear motor as an example,the finite element models with 12 pole,13 pole,14 pole,15 pole and 16 pole matching were established to verify the effectiveness of various thrust wave suppression methods.Finally,a prototype of a 12-pole 36-slot submersible cylindrical permanent magnet synchronous linear motor for oilfield piston pump is tested.Aiming at the problem of excessive thrust fluctuation in the practical application of the linear motor,a multi-objective optimization design was carried out for the two models by changing the pole slot fit and adopting multi-objective genetic algorithm(NSGA-ii).The thrust fluctuation was reduced to less than 5%without reducing the average thrust. |
PDF Full Text Request