720 / 2019-04-25 11:10:21

Contribution of VSC-HVDC to Mutual Ancillary Frequency Support of Adjoining AC Grids

VSC-HVDC; ancillary power control; bidirectional transmission; droop characteristic

To ensure the reliability and power quality of modern integrated high voltage alternating current(HVAC) and high direct current(HVDC) transmission system, conventional ancillary services(AS)is required to adapt to new operation conditions which include the new origin of AS; the new manage manners of system operator(SO); the new division of responsibilities of SO),etc.Thanks to the speed and flexibility , the voltage-source converter-based-HVDC(VSC-HVDC) are expected to the key to fulfill the requirements. A major function of VSC-HVDC is to increase the integration of the various systems and the reinforcement of the internal grid. This paper proposes a coordinated control scheme to allow adjacent AC grids interconnected through VSC-HVDC to provide ancillary services of secondary frequency regulation to each other ,which is implemented by modulating the direction and size of the DC power through the DC link to reach power balance of interconnected AC grids. The flexible function of two-way DC transmission is achieved by controlling the DC voltage at both ends of the DC link with normalizing droop characteristic. Three different work situations are designed in RTDS. The simulation results verify the effectiveness of the proposed control scheme.