LCI Control Strategy of Sensorless EESM Based on Minimum Remainder Commutation Angle

In this article, a load commutated inverter (LCI) control strategy of sensorless electrically excited synchronous motor (EESM) is proposed based on minimum remainder commutation angle to improve the load capacity of LCI. First, the principle of proposed on-load control strategy based on minimum remainder commutation angle is stated, and the LCI natural commutation mode is analyzed. Second, a rotor position and speed estimation method based on field current harmonic at low speed is proposed, which utilizes the existing half-controlled power topology and does not need additional hardware. The band-pass filters and low-pass filter are optimized to simplify the signal processing as well as to reduce the estimation deviation caused by filters. Third, a back electromotive force (BEMF) phase and speed estimation method based on BEMF at high speed is proposed, which can work continuously and accurately in the on-load condition. To avoid the operation shock due to the sudden switching between low- and high-speed estimation methods, a smooth switching algorithm is given, allowing the proposed speed estimation method to run over the entire speed range. Finally, the proposed approach is demonstrated through experiment with a 3.75-kW LCI-fed EESM platform, confirming the proposed estimation method is feasible and the proposed sensorless control strategy can improve the load capacity of the LCI control system.