Influence of synchronous condenser exciter limit on voltage stability of HVDC

Large capacity synchronous condenser can provide strong dynamic reactive power demand for HVDC transmission system, and its operation characteristics are related to excitation parameters. The force excitation voltage ratio and low excitation voltage ratio of synchronous condenser can affect dynamic reactive response and HVDC system voltage. This paper studied the influence of force excitation voltage ratio on voltage stability of HVDC after voltage sag of sending and receiving end, and the influence of low excitation voltage ratio on voltage stability after overvoltage of sending-end caused by DC Bi-polar block fault. The voltage of AC-DC systems, the reactive power of synchronous condenser and transmission power of HVDC are compared under the different excitation limit, respectively. The results show that the output reactive power of synchronous condenser increases by 400MVar and the system voltage increases by 10% of rated value as the force excitation voltage ratio changing from 2 to 3.5 during the process of voltage sag. The recovered time of system voltage of AC system decreases by 3.35s and reactive power of synchronous condenser decreases by 5.14s as the force excitation voltage ratio changing from 2.5 to 3.5. The absorbed reactive power of synchronous condenser increases by 40MVar as the low excitation voltage ratio change from 10% to 0 during the process of DC Bi-polar Block Fault. The results can provide theory basis for the operation of synchronous condenser connected to HVDC.