Impacts of connection and control modes of multi-terminal DC power transmission system on transient stability

The impacts of the connection mode of multi-terminal DC (MTDC) power transmission system on transient stability are analyzed. Research results show that different from parallel connection mode the MTDC system adopting in-series connection mode needs more reactive power and its active power loss is greater, thus the transmission of active and reactive power is more difficult during transient process, so such a connection mode is unfavorable for keeping transient stability of AC/MTDC power system. Taking in-series connection mode for example, the impacts of control modes of MTDC system on transient stability are researched and it is pointed out that constant voltage control and constant current control can slow down the voltage decrease of AC busbar of converter during transient process and it is favorable to prevent the decrease of DC power, therefore the ability of constant voltage control and constant current control in keeping transient stability is better that those of constant power control and constant extinction angle control.