Parallel UPS with a instantaneous current sharing control

Abstract

This paper proposes a novel instantaneous current sharing control scheme ensuring a fast dynamic response and an equal load sharing capability in a parallel connected UPS (inverter). The proposed novel instantaneous current sharing control scheme is based on the instantaneous output voltage control with the current deviation control and the instantaneous current deviation cancellation control utilizing the current share bus circuit. The proposed novel instantaneous current sharing control circuitry employs the share bus signal line interconnecting all the paralleled inverter on a noise insensitive line. The voltage control circuitry forces all the paralleled inverters to share load current, almost equally, by adjustment of the instantaneous reference voltage signal obtained from the current share bus. With the current share bus and the current deviation controller, the paralleled inverter with the highest output current becomes the master inverter; then all the other inverters become slave inverters. The instantaneous output current of the master inverter is subtracted from the other inverters' output currents, and the current deviations in each inverter module are calculated. Hereafter, the instantaneous current sharing controller forces the output current deviations of each inverter to be zero in every switching period. Furthermore, the output reference of the voltage controller is instantaneously to eliminate the unbalanced power. This results in superior power balance performance for parallel operation.