Contents I. Introduction
The integrated starter/generator (ISG) system is becoming increasingly popular in the more electric aircraft owing to its advantages of less weight, volume, and cost [1]–[4]. Although all electric machines have the potential to be ISG, such as permanent-magnet machine, switch reluctance machine, and induction machine, the brushless synchronous machine (BSM) with the merits of mature structure and easy voltage regulation is the only candidate for the generator in the aircraft power system since the 1950s [5], [6]. Although it is employed as the starter for engine cranking, there is no electromotive force induced in the armature windings of the main exciter (ME) with the traditional dc excitation since the rotor speed is low in the initial of the starting. Then, the main generator (MG) cannot be excited and there is no output toruqe [7], [8]. A general single-phase ac excitation is adopted for the BSM, where the field winding of the ME is excited by the ac power, and the ME operates as a transformer to supply the excitation power for the MG in the starting mode. However, the excitation power is limited for output torque of BSM in the starting mode due to the single-phase ac excitation, especially for the high-power engine cranking [9]–[11]. Thus, the three-phase field winding structure of the ME of the BSM has been the commonly used method for the BSM as the starter/generator for the aircraft [12], [13].
