Coordination Control of Commutation Failure Preventions for UHVDC Hierarchical Connection to AC Grid

摘要

The inverters of ultra-high voltage direct current (UHVDC) system are integrated to two voltage levels respectively under hierarchical connection mode. Hence, after AC fault occurs in one of the two voltage levels, the dominant factors inducing commutation failures (CFs) in those two inverters may be different each other. This paper analyzes the dominant factors of CFs in those two sets of inverters. Since the dominant factor of CFs in the inverter connecting to the non-fault voltage level is the increase of DC current, meanwhile the alternating voltage drops mildly. The commutation failure prevention (CFPREV) of those inverters acts so late that it has a low probability of preventing CFs. To address this problem, a coordination control scheme of CFPREVs is proposed to advance the acting time of the CFPREV that acts later by making the CFPREVs act simultaneously. Using the coordination control scheme can effectively prevent CFs of the inverters connecting to the non-fault voltage level. A simulation model based on a planning hierarchical connection project is built in PSCAD/EMTDC. Simulation studies validate the effectiveness of the proposed control scheme.