Emergency power control strategy of HVDC FLC based on modified SFR model in islanded HVDC sending system

Abstract

In the current islanded High Voltage Direct Current (HVDC) sending system for new energy base, with the increase of wind power penetration, the pressure to maintain the frequency stability of the system is increasing. There is a need to use HVDC Frequency Limit Control (FLC) for inter-regional emergency power support. Now, the dead zone (DZ) of FLC is always set to be larger than that of primary and secondary frequency regulation (FR) and maintain a certain margin, which weakens the supporting effect of HVDC on the FR in emergency. Based on the modified System Frequency Response (SFR) model, different disturbance types and sizes can be distinguished in advance by measuring the rate of change of frequency (RoCoF) of system, then a control strategy of HVDC FLC with small dead zone is proposed to deal with disturbances that would lead to large frequency deviation by conventional primary and secondary FR alone. And it will not increase the burden of the HVDC under normal wind power fluctuation. The PSCAD/EMTDC simulation results show that the proposed strategy can effectively improve the frequency stability of the sending system while the drawbacks of traditional FLC is avoided.