To alleviate the problem of line overload raised by the integration of ultra-high voltage direct current(UHVDC)transmission systems

and to enhance the voltage support strength of the AC bus of the UHVDC station

the sensitivities of line loads and AC bus voltage magnitudes to the control of unified power flow controller(UPFC)are deduced based on electrical network theories. Then

the feasibility of the active/reactive power flow control ability of the series converter and the reactive power control ability of the shunt converter to achieve line overload control and voltage regulation is analyzed. On this basis

a UPFC control strategy for power grids integrated with UHVDC is developed. Using this control strategy

the system-level settings of the UPFC are generated automatically based on current/voltage measurements. Finally

a case study is done in the Suzhou southern power grid of China

where the 500 kV UPFC project and Jinping-Sunan UHVDC transmission system are located. The effectiveness of control sensitivity analysis and the feasibility of proposed control strategy are verified in the case study.