Method of In-Phase Connection of Backup Power in Power-Supply Systems with Motor Load

Abstract

A method is proposed for supplying backup power to power-supply systems with induction and synchronous motors that uses in-phase connection of the voltage of backup power source upon group spinning down of motors after emergency loss of the main power supply. Based on the results of mathematical simulation of switching modes of power supply, the permissible regions of phase-shift angles are determined in terms of voltages. In the proposed method, the instantaneous voltages of the main and backup power sources are controlled and the phase-shift angle between the vectors of these voltages is determined. By recording data on the times when the phase-shift angle reaches three predetermined values, a parabolic approximation of the time dependence of the change in the angle is carried out, with the help of which the time that it takes to reach a 360° angle is predicted and, then, taking into account the proper time of activation of the backup power switch, the time to issue the command that it switch on is determined. The results of mathematical simulation and a full-scale test of power switching modes are presented, which confirm the viability of in-phase voltage supply when using the method and a device based on it, making it possible to recommend the method for use in microprocessor-based devices of high-speed automatic power-supply switching.