Reduction of inrush current due to voltage sags by an isolating current limiter
First Claim
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.
4 Assignments
0 Petitions
Accused Products
Abstract
Various systems and methods are provided for minimizing an inrush current to a load after a voltage sag in a power voltage. In one embodiment, a method is provided comprising the steps of applying a power voltage to a load, and detecting a sag in the power voltage during steady-state operation of the load. The method includes the steps of adding an impedance to the load upon detection of the sag in the power voltage, and removing the impedance from the load when the power voltage has reached a predefined point in the power voltage cycle after the power voltage has returned to a nominal voltage.
73 Citations
32 Claims
-
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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 26)
-
-
16. An apparatus for the reduction of inrush current to an electrical load that includes a full-wave rectifier due to short-duration voltage sags on an input AC power voltage, comprising:
-
a sag detector coupled to receive the AC input power voltage, the sag detector operative to provide (i) a signal indicating the beginning of a short-duration sag, and (ii) an altered signal indicating the end of said sag when the AC power voltage applied to the load experiences a short-duration sag during steady-state operation of the load; 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; and a current-limiting circuit coupled between the AC input power voltage and the electrical load that includes a full-wave rectifier, the current-limiting circuit consisting a parallel arrangement of (a) a selectively actuatable relay that isolates the electrical load from the AC power voltage when open, (b) a semiconductor switch in series with a resistance, the current limiting circuit being operative, in response to a signal from the sag detector indicating that a sag has begun, to isolate the AC input power voltage from the electrical load by opening the relay, the current limiting circuit being further operative, subsequent to receiving the altered signal from the sag detector indicating an end of a sag and a zero crossing signal from the zero crossing detector indicating that the AC power voltage has returned to a nominal voltage, to reconnect the AC input power voltage to the electrical load by closing the relay subsequent to turning on the semiconductor switch. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 32)
-
Specification