Rotor Position Estimation Based on Low-Frequency Signal Injection and Estimated Main Field Current for Wound-Field Synchronous Starter/Generator in the Low-Speed Region

Due to the reliability problems of mechanical position sensors, rotor position estimation technology is an alternative for the starting control of aircraft wound-field synchronous starters/generators. Reversible saliency and high-frequency attenuation characteristics of the main machine (MM) may lead to the failure of existing high-frequency signal-based estimation methods. In this article, low-frequency signal (LFS) injection and a novel signal extraction method are combined to estimate rotor position. First, LFS is injected into MM's stator winding, and a response signal containing rotor position information is induced in its rotor field winding. Then, the response signal can be extracted from the estimated main field current (EMFC) by a bandpass filter. Furthermore, the phase of the extracted signal and the injected LFS are obtained by two single-phase phase-locked loops (PLLs), respectively. Then, the increment in the rotor position can be obtained by the two PLLs. Meanwhile, by injecting a specific low-frequency square wave, the initial rotor position can also be extracted from EMFC, requiring no extra pole identification and phase compensation. Finally, by combining the initial rotor position and position increment, a continuous rotor position of MM can be obtained. The effectiveness of the proposed method is verified by experiments.