Magnetic Field Analysis and Operating Characteristics of a Brushless Electrical Excitation Synchronous Generator With DC Excitation

Abstract

To realize brushless excitation for an electrical excitation synchronous generator (EESG), a brushless-induced double electrical excitation synchronous generator (IDEESG) with dc excitation is investigated in this study. The static magnetic field is established by injecting dc into the stator excitation windings that are added in the stator slots. Rotor windings are divided into two parts: induction coils and rotor excitation winding. The induction coils cut the static magnetic field and provide dc current for the rotor excitation winding after the rectification. The direction of the currents in the induction coils is constant because of the half-wave rectification. The magnetic flux generated by the currents in the induction coils and rotor excitation winding is added in the air gap to induce the armature coils in the stator. In this study, the structure and the operating principle are examined. The frozen permeability method is adopted to study the influence of the currents in the induction coils and the rotor excitation winding on the magnetic field distribution. The harmonic content of currents in the induction coils is analyzed using the Fourier series form and the effect of the harmonics on the output voltage is also studied. A 1.5 kVA prototype is fabricated to verify the correctness of theoretical analysis and simulation.