Patent ID: 9065266
Filing Date: 2015-06-23
Classification: H01H,H02H

Abstract:
1. A method for the reduction of inrush current to an electrical load that includes a full-wave rectifier due to short-duration voltage sags on an AC input power voltage, comprising the steps of: providing a current-limiting circuit coupled between the AC input power voltage and an electrical load that includes a full-wave rectifier, the current-limiting circuit consisting of a selectively actuatable relay connected in parallel with a series combination of a semiconductor switch and a resistance, wherein the selectively actuatable relay presents an infinite resistance when open to isolate the electrical load and a path of least resistance between the AC input power voltage and the electrical load when closed; providing a sag detector coupled to receive the AC input power voltage, the sag detector providing a (i) signal corresponding to a beginning of a short-duration sag, and (ii) an altered signal corresponding to an end of said sag in the AC input power voltage during steady state operation of the electrical load; providing a zero crossing detector coupled to receive the AC input power voltage, the zero crossing detector operative to provide a zero crossing signal in response to detection of a zero crossing in the AC input power voltage; applying the AC input power voltage to the electrical load through the relay in the current-limiting circuit; in response to receiving the signal from the sag detector indicating that a short-duration sag has begun, isolating the AC input power voltage from the electrical load by opening the relay; when the AC power voltage has returned to a nominal voltage, receiving the altered signal from the sag detector indicating an end of the sag; in response to the altered signal from the sag detector and in response to the zero crossing signal from the zero crossing detector indicating that the AC power voltage has reached a predefined point in the power voltage cycle, reconnecting the load to the AC input power voltage by turning on the semiconductor switch so that the current to the load flows through the resistance; and subsequent to turning on the semiconductor switch, closing the relay so as to reconnect the AC input power voltage to the electrical load.