Contents I. Introduction
As one of the core technologies of more electric aircraft (MEA), the integrated starters/generators (ISGs) with the combination of the traditional starter for engine cranking and electrical power generation have the obvious advantages in weight and volume reduction, and the system architecture could also be simpler and more reliable [1], [2]. As the candidates of the ISG in the aviation applications, such as a three-stage synchronous machine (TSM) [3]–[5], a permanent magnet synchronous machine (PMSM) [6], [7], and a switched reluctance machine (SRM) [8], [9], TSM with the property of mature structure and simple control in generation mode has been most attractive in the realization of the integration of start and power generation, while, due to the combination structure with the permanent magnet auxiliary exciter, main exciter (ME), and main generator (MG), in order to achieve the engine cranking, the ac excitation with different windings arrangement methods should be applied to the ME [10], [11], and the accurate rotor position information is also acquired for MG in the starting control. Thus, the additional rotor position sensor should be installed for the TSM, while it will increase the axial size and the complexity of the rotor structure of TSM, and the corresponding power density and reliability will also be decreased. Besides, the complex environment and serious operating conditions of high-temperature, high-pressure, and high-intensity vibration will further deteriorate the accuracy and reliability of the position sensor and even cause damage. Moreover, since the starting operation just takes several minutes for engine cranking, then TSM works in the generation mode, which is the long-time running condition, where the rotor position sensor is not necessary.
