An LCI Controller for Single-Phase Brushless Exciter Synchronous Motors With Extended Operating Range

This paper proposes a modified field-oriented control scheme for load commutated inverter-fed synchronous motors with single-phase brushless exciters. The core novelty is a fully analytical, real-time calculation of the inverter firing angle embedded directly into the control loop, eliminating the reliance on static margin angles, simplified speed estimations, empirical look-up tables or external hardware sensors. Specifically, the proposed scheme: 1) improves pulse generation accuracy through a load-synchronized firing scheme based on estimated stator fluxes; 2) effectively regulates rotor speed and stator flux magnitude using a simplified brushless exciter model; and 3) extends the speed and torque operating range by continuously adapting the firing angle to the instantaneous load current and commutation inductance without requiring offline calibration. Consequently, this analytical formulation minimizes unnecessary safety margins, reducing overall average exciter field and stator currents, allowing the extension of speed and torque operating range. Hardware-in-the-loop tests validate the robust dynamic response under a typical milling load profile.