Permanent Magnet Linear Alternator Magnetic Field Analysis

Permanent magnet linear alternators are energy converting devices that have been under research and development for years. This type of alternators have advantages of high efficiency and no need of liner motion to rotation converting, when the driving force is in linear oscillation. Such applications can be found when ocean tide, solar power, and swing motions are used for generating electric power. Magnetic field analysis is essential for electric machine designs. Results from the analysis provide the magnetic field distributions in a machine. Magnetic field analysis may help the designer to modify their design for getting a better product. Magnet field analysis may also be used for finding torque, force, power losses, and induced voltage, which are the primary parameters of electrical machine performance study. This paper presents the magnet field analysis of a cylindrical permanent magnet linear alternator. This alternator has four permanent magnet rings mounted on a plunger (shaft), which oscillates linearly when the machine is working. The magnetic polarities (N pole or S pole) of the rings are in radial direction and the polarities alternate from one ring to the next on each side of the plunger. Two of the magnet rings are on each end of the plunger and a magnetic loop is formed by the permanent magnet rings, plunger, stator core, and the air gap between plunger and stator core. The stator core is an iron structure surrounding the plunger, magnet rings, and the stator winding. When the plunger is at one end position of its oscillation, one stator pole faces to an N pole of a magnet ring and the other stator pole faces to an S pole of another magnet ring. When the plunger moves to the other end position of its oscillation, the magnet ring polarities face to the stator poles are switched. Therefore, the magnetic flux in the loop changes its value and direction for each cycle of the plunger oscillation. The stator winding, which is a circular coil around the plunger and inside of the stator core, experiences the flux changes and generates AC power. In this research, the magnetic filed study was conducted with Maxwell software, which is a product of ANSYS Company. The magnetic filed distributions for different positions of the plunger and different space gap between magnet rings were investigated. The results from the research are presented and discussed in this paper.