Initial Rotor Position Estimation Method for a Wound-rotor Synchronous Starter/Generator Based on Voltage Pulse Injection and Fourier Fitting

The traditional initial rotor position estimation method is not applicable to a wound-rotor synchronous starter/generator due to the large variation of inductance parameters and the instability of rotor excitation flux of the main generator (MG) of three-stage synchronous starter/generator (WRSSG). In order to improve the estimation accuracy, this paper proposed a voltage pulse injection method by comparing the peak of three-phase induced currents for initial rotor position estimation. The influence of different amplitudes of injected voltage pulses on the waveform of peak currents was studied based on the relative size of dq axis inductances. Accordingly, the injected voltage and excitation voltage were chosen properly to achieve an accurate estimation of the initial rotor position and to eliminate the polarity detecting process. Moreover, a current waveform fitting method by using Fourier series was proposed to compensate the estimated error brought by the unsteady rotor excitation flux. The third-order Fourier series, which was the most suitable order of Fourier series to fit the current waveform, was obtained. With these improvements, the accuracy of initial rotor position estimation was improved and the proposed method was of good robustness. Finally, all the theoretical analyses were validated by experiments on a laboratory 75kW WRSSG. © 2022 Chin. Soc. for Elec. Eng.