| Compared with linear drive systems constructed by rotating electrical machines, linear electrical machines have many favorable features, like simple structure, high control precision, no centrifugal forces, et al. However, the drawback of low force densities has limited their applications in high-performance linear servo systems. By applying the transverse flux configuration to linear machines, high force density can be achieved, which is of great significance to the development of linear systems. In this thesis, a novel tubular transverse flux Permanent Magnet Linear Machine (PMLM) is put into focus, and the problems of electromagnetic field computation, inductance computation, and electromagnetic force analysis have been studied.Aimed at traditional transverse flux machines, the magnetic circuit and its features are analyzed, and the operating principle is brought forward according to PM's surface current model. The results show that if the field generated by armature currents is regarded as the air-gap magnetic field and the PM is represented by surface current, the electromagnetic force can also be analyzed with Lorentz Law. Based on them, a novel tubular transverse flux PMLM is proposed. By taking steel laminations, the proposed tubular transverse flux PMLM is easy to manufacture and thus can overcome the shortcomings of traditional transverse flux machines, like complex structure, weak construction, et al.According to the features of the machine structure, the computation model is simplified, and the electromagnetic field of the tubular transverse flux PMLM is computed by 3-D Finite Element Method (FEM). The influences of PM magnetization length and axial length of stator segment on no-load main flux linkage are then studied. The results show that the no-load main flux linkage does not increase all along with the increase of the two parameters. Aimed at the problem of large leakage flux, auxiliary cores are inserted between stator segments to eliminate the leakage flux between PM, and the influence of axial length of the auxiliary core on no-load main flux linkage is also computed. And then the edge effect is analyzed, and the result shows that the edge effect makes the three phases asymmetric and would have an impact on the steady operation of the machine. The back-EMF of the tubular transverse flux PMLM at variational speed is tested by detecting the real-time speed signal.Aimed at complex computation of the inductance of the prototype, by computing the total inductance of one element machine, end-winding inductance and the leakage inductance between stator segments and then combining them, the inductance of the prototype is obtained. The comparison of the experimental result and FEM result has confirmed the correctness of this method. Based on it, the problem of magnetic coupling between phases is analyzed, and the result shows that the three phases of the tubular transverse flux PMLM are basically decoupled, which provides formula for simplification of performance analysis. And then the influence of armature current to the winding inductance is studied. The results show that the armature current not only influences the numerical value of the inductance, but also the waveform, mainly embodying that the inductance varies two periods within an electrical cycle when the current is small and it varies one period when the current is large.With virtual work method, the cogging force and mutual force are theoretically analyzed. An equivalent 2-D model is proposed to compute the cogging force, and the comparison of the obtained results, via 2-D and 3-D FEM analysis, has proved the validity of the equivalence. Based on it, the influence factors of the cogging force are analyzed and the cogging force is reduced effectively. The mutual force characteristics are computed and analyzed at different operating modes, and the influences of parameters on the mutual forces are also studied. And then the influence of edge effect on the electromagnetic forces is analyzed. The results show that the edge effect causes the pulsation of the thrust force and thus make an impact on the calmness of the thrust force. The experimental results of cogging force and mutual force have proved the correctness of the computation and analysis above.
|
PDF Full Text Request