New digital control of forced commutation HVDC converter supplying into load system without AC source

The authors describe a digital control technique for a forced commutation converter applied to HVDC transmission systems with loads which have no AC sources. The technique used direct calculation of the firing angle of the inverters. The results of simulator experiments and computer simulations show good performance for the regulation of the AC voltage of a load system without an AC source. In particular, it works well when a ZnO arrester is installed to suppress overvoltage which occurs when the load in the receiving system is suddenly rejected. The results show that the control technique drastically shortens the overvoltage duration and decreases the amount of energy absorbed by a ZnO gapless arrester installed at the inverter station