The separate control layer is in the same class as the valves
control layer in the control level. It receives the instruction
from converter control layer to control all kinds of devices
except valves itself, for example, converter transformer shift
switch control [16], filters on/off control, cooling the valves
auxiliary control, monitoring the state of the equipment in
converter station, meanwhile, it feedbacks message to the
converter control layer. While the control equipment
confronting jeopardize, it will trigger the automatic control and
protection system.