Investigation of HVDC link under constant power control

Recently high voltage de systems (HVDC) become more popular in transmission of bulk powers. Most of the interconnecting links between large and long transmission networks are HVDC links. This paper illustrates a developed technique to maintain constant power during severe voltage sag at the sending end. This technique depends upon a constant reference power which determines the value of reference current in the link, when using constant current control (C.C) at the sending end and constant extinction angle control (C.E.A.) at the receiving end with a distinct voltage dip or sag in the sending end voltage, a run down [1] will occur. On the application of minimum ignition angle (α min) to the rectifier side and by controlling the voltage at the inverter side a dc current in the HVDC link can be controlled to maintain constant link power even the transformer tap changers restore converter quantities. By this technique it is possible to prevent a run down to the link which reflects on the national income of the country.