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|1. (WO2018076904) FAULT CURRENT LIMITING CONTROL AND PROTECTION COORDINATION METHOD FOR CONVERTER OPERATING IN ISOLATED STATE IN FLEXIBLE DIRECT CURRENT POWER TRANSMISSION SYSTEM|
|Applicants:||NR ELECTRIC CO., LTD
NR ENGINEERING CO., LTD
|Title:||FAULT CURRENT LIMITING CONTROL AND PROTECTION COORDINATION METHOD FOR CONVERTER OPERATING IN ISOLATED STATE IN FLEXIBLE DIRECT CURRENT POWER TRANSMISSION SYSTEM|
A method for fault current limiting control and protection coordination for a converter operating in an isolated state in a flexible direct current power transmission system: a converter output current limiting command Imax for use in restricting a size of a current command L*Ldq of a current inner loop dq; during alternating current system fault, Imax is set to be equal to a numerical value of an alternating current line overcurrent protection section III or slightly greater than a numerical value of an overcurrent protection section III; a constant value of an alternating current line overcurrent protection section I is set to be lower than a constant value of a converter bridge overcurrent protection section I; when a numerical value of a converter bridge overcurrent protection section II is lower than a numerical value of an alternating current line overcurrent protection section II, or when the numerical values are equal, the converter bridge overcurrent protection section II has a longer time delay compared with that of an alternating current protection section II; when detecting a fault on a connection line side of the converter, a current restricting command numerical value Imax of the converter is switched from a normal allowable output current multiple to a numerical value of the alternating current line protection section III during fault; by means of restricting the size of the converter output current, part of a short-circuit current is provided, and alternating current fault is cut off by means of the alternating current line protection section III without affecting normal operation of the converter; after an alternating current side fault is cut off, Imax is restored to an allowable output current multiple of the converter under normal conditions. The Imax switching method is to detect a voltage amplitude of a network side in real time, and, according to the voltage amplitude, to use an interpolation method or a look-up table method to obtain the current command restricting value Imax for use in limiting the size of converter output current when operating in a passive state according to preset n groups (ULj, Imaxj)(j＝1, 2…n) of a two-dimensional numerical value sequence or curve.