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1. (WO2018104434) IMPROVEMENTS IN OR RELATING TO LINE COMMUTATED CONVERTERS

Pub. No.:    WO/2018/104434    International Application No.:    PCT/EP2017/081794
Publication Date: Fri Jun 15 01:59:59 CEST 2018 International Filing Date: Fri Dec 08 00:59:59 CET 2017
IPC: H02M 1/32
H02M 7/5387
Applicants: GENERAL ELECTRIC TECHNOLOGY GMBH
Inventors: SHE, Xu
BARKER, Carl D.
DAVIDSON, Colin Charnock
Title: IMPROVEMENTS IN OR RELATING TO LINE COMMUTATED CONVERTERS
Abstract:
In the field of high voltage direct current (HVDC) power transmission a line commutated converter (10) includes a plurality of converter limbs (12A, 12B, 12C) that extend between first and second DC terminals (16, 18). Each converter limb (12A, 12B, 2C) includes first and second limb portions (22, 24) that are separated by an AC terminal (26). The first limb portions (22) together define a first limb portion group (28) and the second limb portions (24) together define a second limb portion group (30). Each limb portion (22, 24) includes at least one switching element (32) in the form of a latching device (34). Each latching device (34) is configured to turn on and conduct current when it is forward biased and it receives a turn on signal, to naturally turn off and no longer conduct current when it is reverse biased and the current flowing through it falls to zero, and to actively turn off and prevent current from flowing therethrough when it receives a turn off signal. The line commutated converter (10) also includes a control unit (38) that is programmed to control switching of the latching devices (34). The control unit (38), during normal operating conditions, successively sends a first latching device (34) in a respective pair of first and second latching devices (34) in one of the first limb portion group (28) or the second limb portion group (30) a turn on signal whereby the first latching device (34) turns on and begins to conduct current while the current flowing through the second latching device (34) begins to fall to zero and the second latching device prepares to naturally turn off. The control unit (38),in the event of abnormal operating conditions arising, sends a turn off signal to the or each latching device (34)experiencing an abnormal current flow therethrough to actively turn it off and prevent current from flowing therethrough.