A Series Voltage Compensated Synchronous Motor Drive With Load Commutation During Starting and Low-Speed Operation

A major problem faced in the conventional load-commutated current-source inverter (CSI)-fed synchronous motor drive is the commutation failure during low-speed operation due to insufficient back EMF. The scheme adopted by the industry as a solution to this problem is to employ pulsed mode operation during starting and at low speed. However, the pulsed mode operation results in undesirable high-torque pulsation. This article proposes a new scheme to facilitate hassle-free load commutation of CSI-fed synchronous motor drives during starting as well as at low speed without resorting to pulsed mode operation. The proposed scheme consists of an open-end winding synchronous motor with silicon controlled rectifier (SCR)-based CSI connected to one side of the stator windings and an IGBT-based voltage-source inverter (VSI) connected to the other side to aid commutation of SCRs when the back EMF is insufficient. The proposed scheme is experimentally verified on a 3-HP synchronous motor drive using a digital signal processor (TMS320F28335) for the implementation of the control scheme.