Influence of the axial-length ratio of permanent magnet to homopolar induction on the performance of hybrid excitation synchronous generator

Magnetic flux distributions of the permanent magnet (PM) section and the homopolar induction (HI) section in a hybrid excitation synchronous generator (HESG) are calculated by using the finite element method (FEM). The influences of the axial-length ratio of the two sections on the back EMF, inductance, and terminal characteristics of the PM section, the HI section, and the HESG are analyzed. The prototype experiments have verified the validity of the calculation and analysis processes. The studies on the HI section have shown the following: 1) The operating air-gap flux distribution along the axial direction is uneven; 2) there is an approximate linear relationship between the radial component average of the operating air-gap flux density and the axial length; 3) a quadratic relationship between the back EMF and the axial length exists; and 4) it is necessary to compute and optimize the axial-length ratio of the PM section and HI section to increase the output voltage and improve the terminal characteristics of the HESG.