Fault current limiting control and protection coordination method in stand-alone operation of flexible DC transmission system converter

摘要

Fault current limiting control and protection coordination method of the flexible DC power transmission system in a standalone operation. The converter output current limit command Imax is for limiting the magnitude of the current command L ^*_Ldq of the current inner loop dq. Imax is set equal to the overcurrent protection stage III value of the AC line or slightly larger than the overcurrent protection stage III value, and the overcurrent protection stage I setting of the AC line is set smaller than the overcurrent protection stage I setting of the converter bridge arm. However, if the overcurrent protection stage II of the converter bridge arm is lower than or equal to the value of the overcurrent protection stage II of the AC line, the delay time is longer than the stage II protection. When a converter connection line fault is detected, the converter current limit command Imax is converted from the converter allowable output current multiple under normal conditions to the faulted AC line protection stage III value, limiting the converter output current magnitude, thereby limiting some short circuit current. The AC line's overcurrent protection stage III eliminates AC faults and does not affect the normal operation of the converter. After the AC side fault is eliminated, Imax is restored to the converter's allowable output current multiple under normal circumstances, but the switching method of Imax detects the voltage amplitude value on the grid side in real time, the magnitude of the voltage amplitude value and the preset n groups According to the two-dimensional numerical series or curve of (U _Lj , Imaxj) (j = 1, 2… n), current command to limit the output current magnitude when the converter is operating in passive state using interpolation or table lookup method Obtain the limit value Imax.