Overshoot Damping Control of DC Current at Deblock in AC-DC Interconnected System with Externally Commutated Converters

Abstract

Deblock of AC-DC interconnected system with externally commutated converters generally adopts soft start which makes trigger delay angle about 90 degrees and starts DC voltage from about 0kV. High DC voltage, however, is possibly caused by relation between the deblock signal and AC voltage phase at the commutation start of converter, resulting to overdue current. Consequently, overshoot of DC current is generated and transient AC voltage sag is caused especially under the condition of relatively weak AC system.
We resolved the generation mechanism of DC current overshoot at deblock. In addition, we reflected the mechanism in the control system of Higashi-Shimizu FC, and drew up overshoot damping control by EMTP simulation. Furthermore, we checked the effect of overshoot damping control at the commissioning test period and verified that result of measurement corresponded with EMTP simulation.