Blocking and deblocking strategy of single UHVDC converter group under joint control mode of dual 12-pulse converter groups

The blocking and deblocking strategy of single converter group under the joint control mode of dual 12-pulse converter groups is studied with PSCAD / EMTDC for UHVDC power transmission system. The sequential control and timing coordination of firing angle,ignition pulse,bypass switch,bypass pair and online controller parameter adjustment are analyzed. Simulative results show that,the deblocking of single converter group should adopt small firing angle under the joint control mode of dual 12-pulse converter groups and the rate limiter and value limiter should be added in series after the firing angle limiter is disabled to improve the dynamic performance of DC operating parameters during the deblocking;while during its blocking,the firing angle should be adjusted to 90° at a certain rate and the bypass pair should be put into operation to speed up the blocking process. Case studies show that the proposed strategy meets the requirements of UHVDC single converter group blocking and deblocking operations.