An Envelope-Prediction-Based Sensorless Rotor Position Observation Scheme for LCI-Fed EESM at Zero and Low Speed

An envelope-prediction-based sensorless rotor position observation scheme is proposed for a load commutated inverter (LCI)-fed electrically excited synchronous motor (EESM) at zero and low speed. The proposed rotor position observation scheme does not need to utilize the full controlled power device, nor to modify the LCI drive topology. An interval trigger mode for the exciter control is proposed to generate the appropriate fixed-frequency injected signal. The bandpass filters (BPFs) are optimized to extract the target signal, and the observation error due to the BPF is analyzed and compensated. A specific signal sampling method and an envelope-prediction algorithm are presented to simplify calculation and improve the observation accuracy. A normalized phase-locked loop is designed such that the observer has a better observational performance. Finally, the proposed rotor position observation scheme is verified by a 15-kW LCI-fed EESM experimental platform.