Analysis Of Free-piston Permanent Magnet DC Linear Generator Used For Internal Combustion Engines

The power system used for series hybrid vehicle drive system consists of free-piston engine and permanent magnet linear generator. It can overcome the disadvantage of the system which is composed of engine crankshaft connecting rod and rotating generator. The new system can improve fuel efficiency and reduce harmful emissions.A novel free-piston permanent magnet DC linear generator structure is proposed in this paper. The generator is cylindrical. And the permanent magnets are magnetized radically and adhered on the mover's bracket. The internal stators are fixed at the external stators'brackets through the mover's bracket. Viewed from the stator, the mover has only one magnetic pole. The stator is winded with one set of windings in series. When the permanent magnet moves in one direction, the direction of EMF is unchanged. The proposed generator operates in the same manner as a DC permanent magnet linear generator.Because of asymmetry along the axis of the generator, three-dimensional model is constructed by analysis of three-dimensional finite element. The basic dimensions are determined and such datas as the inductance, EMF, and electromagnetic thrust are also calculated in this paper, which indicate the generator performance. The parameters are optimized repeatedly in order to meet the requirements. The generator is a semi-closed magnetic circuit structure. The armature reaction magnetomotive force generated by the coil and the permanent magnetomotive force generated by the permanent magnet will influence mutually and lead to magnetic saturation. So it's necessary to set the adjusting ring of magnetic circuit to improve the status of magnetic saturation.It's a effective way to reduce cogging force fluctuation by analysis of cogging force, decomposing the cogging force and optimizing the length of mover according to Fourier decomposition results. And it can be concluded that the minimum cogging force of the single-pole semi-closed magnetic circuit permanent magnet linear generator is regular.