A Novel Flux Observer and Switching Scheme for LCI-fed Synchronous Motor Drives

Load-commutated inverters (LCIs) with wound-field synchronous motors (WFSMs) form one of the most applicable drive topologies, and in some cases the only one, in high-power medium-voltage applications. In this paper, a novel method is introduced to determine the switching instants of the thyristors which is done through the stator flux estimation. Compared to other frequent switching schemes, the proposed method is simple, less parameter sensitive and free from some additional circuits or transducers. Also, a comprehensive flux observer is presented to estimate the stator fluxes. Some disadvantages concerning the other flux observers such as initial conditions and dc drift problem, large time constant at high speeds and phase and magnitude error in low speeds are eliminated by the proposed observer. Simulation results show the validity of the proposed switching scheme and flux observer in a wide speed range.