Patent ID: 8305783
Filing Date: 2012-11-06
Classification: H02H

Abstract:
1. An inrush current protection circuit for a polyphase alternating current power system, the circuit comprising: a plurality of current limiting resistors, each of the plurality of current limiting resistors electrically coupled in series between a respective one of a plurality of phases of a polyphase alternating current power source and a respective input of a polyphase transformer rectifier unit; a plurality of first power switches, each of the plurality of first power switches electrically coupled in parallel with a respective one of the plurality of current limiting resistors, such that when each of the plurality of first power switches is closed, essentially no electrical current flows through the respective one of the plurality of current limiting resistors, and when each of the plurality of first power switches is open, electrical current flows through the respective one of the plurality of current limiting resistors; a plurality of second power switches, each of the plurality of second power switches electrically coupled in series between a respective one of the plurality of current limiting resistors and a respective input of the polyphase transformer rectifier unit; and a power switch controller configured to control each of the plurality of first power switches to be open such that when the polyphase alternating current power source is applied to the inrush current protection circuit, an inrush current passes through the respective one of the plurality of current limiting resistors rather than the respective first power switch, and to be closed after a first time delay has passed, the power switch controller further configured to control each of the plurality of second power switches to be open such that when the polyphase alternating current power source is applied to the inrush current protection circuit, a power-on transient of the polyphase alternating current power source does not reach the polyphase transformer rectifier unit, and to be closed after a second time delay has elapsed, the second time delay being shorter than the first time delay such that the plurality of second power switches are closed before the plurality of first power switches are closed.