Design and Excitation Control of a Dual Three-Phase Zero-Sequence Current Starting Scheme for Integrated Starter/Generator

A harmonic excitation brushless synchronous machine has higher power density compared with the traditional aerial three-stage generator due to removing the axial exciter and is suitable for use as an integrated starting-generator (ISG). However, the field current cannot always be generated in the field windings at different rotor positions in the starting mode. A new excitation scheme employing double three-phase phase orthogonal zero-sequence armature currents is proposed in this article. Harmonic electromotive forces and field current can be produced by the zero-sequence rotating excitation magnetic field and almost has no relationship with the rotor positions. In addition, in order to obtain a constant field current during the starting process, a control method of the generated field current is also presented. The rotating speed and field intensity of the zero-sequence excitation magnetomotive forces are both feedback controlled by the zero-sequence current in the whole starting process. Comparing with the original harmonic excitation machine, a higher and more stable field current can be generated in the proposed ISG whenever the rotor is at any position or at a low speed. The prototype machine is manufactured and experiments are carried out together with the excitation control method to verify the effectiveness of the theoretical and finite element analysis results.