Characteristics Study Of A Novel Linear Permanent Magnet Vernier Synchronous Motor

Permanent magnet linear synchronous motors (PMLSM) have many advantages, such as big thrust, fast response, simple structures, easy maintenance, etc., it can be applied widely in linear motion occasions. As the development of science and technology, the theoretical study of PMLSM is more and more deeply, it mainly has the following three defects. First, the motor speed that is relatively high is difficult to reduce under the industrial frequency power conditions, and the performance of PMLSM becomes poor under low frequency. Second, to reduce its speed under the condition of constant frequency, we need to increase its pole pairs. Third, the detent force in PMLSM is very large, which causes the thrust ripple and affects the steady operation performance of the motor, this phenomenon is more apparent during low speed operations. In order to overcome these shortcomings, with the motor volume and slot number unchanged, the traditional structure of PMLSM is improved, a new type of linear permanent magnet vernier motor (LPMVM) is proposed. The characteristics of the proposed motors are low speed under power frequency or high frequency, simple structure, reduced thrust ripple, and improved performance. The main research content of this thesis can be summarized as follows:The magnetic circuit theories of LPMVM are analyzed. Different from traditional structure and principle of PMLSM, the fundamental wave and harmonic magnetic field produced by PM are computed according to the air-gap permeance method if only stator slotted. The structure parameters and speed relationship among the stator slot numbers, stator winding pole numbers and PM numbers are gotten when the synchronous thrust is produced. We expound its working principle by comparing the magnetic field distribution of the motor before and after moving a certain distance. We have the conclusion that the fundamental amplitude and the Gr order harmonic are working harmonics, the fundamental amplitude of PM flux density is less than the Gr order harmonic amplitude of it. By winding function theory, the thesis has deduced the formulas of no-load EMF and thrust which have the relation with the fundamental wave and harmonic magnetic field, and carried out a comparative analysis with the electromagnetic performance of the traditional PMLSM.Two-dimensional air gap relative permeance function method is used to consider the influence of the slot effect and the magnetic field layered analytical model of LPMVM is established. The air-gap magnetic field is equivalent to the combined action of slotless magnetic field and air gap relative permeance function. The analytical expressions of slotless layered model with the magnetic vector potential that PM and armature act on each region respectively are derived according to each layer interface boundary conditions. By Schwarz-Christoffel transformation, the thesis has established the analytical model of relative permeance function considering the slot effect. The results of analytic method and FEM show that the air gap flux density of slotless model along the tangential component and normal component are both agree with very well, but the tangential component has large error when considering the slot effect, so the air gap relative permeance function fails to consider the slot effect on the tangential direction of the magnetic field.In view of the limitations of air gap relative permeance function, accurate subdomain model of LPMVM is proposed. In order to consider PM relative permeability, slot depth, the influence of interaction between slots on the magnetic field, the accurate subdomain model of LPMVM that is more close to the actual situation is proposed, scalar magnetic potential Laplace’s equations are applied to analyse three different kinds of regions, that is, slot, airgap and PMs subdomains. By applying the boundary conditions on the interfaces between subdomains, the Fourier series decomposition is applied to derive each boundary condition matrix equations, predict the analytic magnetic potential and flux density based on subdomain model. The FEM results have verified the feasibility and precision of the accurate subdomain model.Electromagnetic parameters and operating characteristics are analyzed according to analytical flux density expressions of the LPMVM based on accurate subdomain model. Ignored the end effect, Maxwell stress tensor method is used to deduce the slot force and vertical force expressed by the harmonic amplitude of flux density, the conclusion is proved by FEM when the mesh of airgap is refined reasonably. The expression of no-load EMF, static thrust under constant current source and steady state thrust are given, the investigation shows that thrust is large and the force ripple is very small, while the analytical results is validated by the FEM results. The equivalent circuit of LPMVM is established, the electromagnetic performance of the motor and its steady state performance are analyzed. Self inductance and mutual inductance of the motor windings are calculated by flux linkage method when armature current acts alone, also the synchronous inductance, leakage inductance, and armature reaction are deduced by dq coordinate transform. The thesis calculates its electromagnetic performance such as armature current, power, thrust, efficiency and power factor, computes the power-angle characteristic and current versus power-angle curve by analytic method and FEM while the resistance is considered, the analytical results are basically the same with the FEM method. The effect on the maximum electromagnetic power and thrust are also discussed when the voltage and frequency changed. Time-stepping FEM is used to analysis the motor transient performance, the results show that the thrust ripple and speed fluctuation are relatively small in low speed. The results of thrust, speed and current by FEM under the power-angle of different steady state are consistent with theoretical analysis.The minimum of detent force is studied by optimizing the end tooth length method. Based on a short primary type LPMVM, the equivalent model of end component is used to simulate the end effect, and the magnetic field analytical model of end component is established. According to the principle of optimizing the length of mover, the thesis deduces formulas of the minimum detent force so as to determine the predicted end tooth width, then parameterizes end tooth width near the referenced value to determine its exact value for minimum detent force, and improves the computation efficiency. The optimized structures mainly reduce the fundamental wave of end force, and the performance of motor is improved.