Soft-starting techniques for low cost single-phase to three-phase drive system configuration

This paper aims to propose solutions for mitigating the adverse effects of starting torque transients, especially in low cost single-phase to three-phase drive systems. The first approach employed for reducing hard current transient and troublesome torque is based on Steinmetz connection; this minimizes the currents of negative sequence and uses the grid source in series with the converter. The second proposal uses the midpoint of dc-link capacitors. The motor starts in a configuration that allows three-phase control, an efficient soft start and the power factor control, as well. Several relevant characteristics of the proposed strategies are addressed. Simulated and experimental results are presented to validate the proposed approaches.